vNYD 


THE  CLIMAX  OF  SCIENTIFIC  ACHIEVEMENT — CONQUEST  OF  THE  AIR 
American  air  squadron  over  San  Diego,  California 


EVERYDAY   SCIENCE 


BY 

WILLIAM    H.    SNYDER,   Sc.D. 

PRINCIPAL  OF  THE  HOLLYWOOD   HIGH   SCHOOL 
LOS  ANGELES 


ALLYN   AND   BACON 

BOSTON  NEW  YORK  CHICAGO 

ATLANTA  SAN  FRANCISCO 


COPYRIGHT,  1919,   BY 
WILLIAM   H.  SNYDER 


NotfaooB  tfrese 

J.  S.  Gushing  Co.  —Berwick  <fe  Smith  Co. 
Norwood,  Mass.,  U.S.A. 


-Vb 


PREFACE 

EVERYDAY  SCIENCE  was  written  primarily  for  eighth  and 
ninth  grade  pupils  who  will  never  have  any  further  training 
in  science.  The  book,  therefore,  covers  a  wide  field,  and 
does  not  unduly  emphasize  any  of  the  special  sciences.  The 
subject  matter  is  chosen  not  for  the  purpose  of  appealing 
to  any  group  of  special  science  teachers,  but  rather  with  a 
view  to  making  pupils  as  intelligent  and  useful  citizens  as 
possible. 

The  book  is,  first  of  all,  both  interesting  and  simple,  and 
aims  not  only  to  furnish  a  fund  of  valuable  scientific  infor- 
mation, but  also  to  arouse  scientific  curiosity  and  to  en- 
courage further  study  both  in  and  out  of  school.  It  will 
inculcate  scientific  habits  of  thought,  and  will  substitute 
the  beginnings  of  knowledge  and  confidence  for  misappre- 
hension and  superstition. 

The  usefulness  of  science  is  brought  out  in  innumerable 
applications  of  its  principles  to  the  household,  the  yard  and 
garden,  the  farm,  the  city  street,  industries,  and  transpor- 
tation. Good  citizenship  is  fostered  by  the  interesting 
treatment  of  such  subjects  as  personal  hygiene,  community 
health  and  sanitation,  reclamation  of  lowlands,  irrigation, 
forestry,  coastal  navigation,  canals,  and  inland  waterways. 

But  the  pupil's  scientific  studies  are  not  hemmed  in  by 
the  four  walls  of  the  home,  by  the  garden  fence,  or  even  by 
the  nation's  boundaries.  Breadth  of  vision,  imagination, 
and  reverence  are  cultivated  by  a  knowledge  of  the  earth 
as  a  planet,  of  the  main  outlines  of  its  physical  history,  of 
ill 


IV  PREFACE 

its  neighbors  in  limitless  space,  and  of  the  changeless  laws 
that  govern  its  relations  with  the  heavenly  bodies. 

The  pupil  is  never  plunged  into  discussions  that  are  beyond 
his  depth.  Long,  intimate  experience  with  young  students 
has  shown  how  futile  it  is  to  presume  any  background  of 
scientific  information  on  the  part  of  eighth  and  ninth  grade 
pupils.  From  the  very  beginning  the  book  proceeds  from 
the  known  to  the  unknown,  from  the  more  simple  to  the  less 
simple.  It  may  be  taught  in  its  entirety  to  immature 
pupils. 

To  make  the  various  subjects  more  vivid  and  more  in- 
teresting, practically  every  topic  is  illustrated  either  by  a 
photograph  or  by  a  drawing  or  by  both.  The  many  ex- 
periments help  to  fix  the  principles  and  to  inculcate  scien- 
tific habits  of  thought. 

The  present  edition  contains  sixty  simple  projects  which 
will  appeal  to  boys  and  girls,  and  which  can  easily  be 
worked  out  without  the  use  of  expensive  material. 

Thanks  are  due  to  the  many  teachers,  especially  in  Los 
Angeles,  whose  suggestions  have  helped  to  make  the  book 
both  teachable  and  learnable. 

JULY  4,  1919.  \y.  JJ,  g. 


CONTENTS 


The  two  opening 
chapters  orient  the 
pupil  in  the  universe. 
Figuratively  speaking, 
the  author  takes  him 
up  on  a  high  mountain, 
lets  him  survey  the  field, 
and  helps  him  get  his 
bearings  in  the  world. 


CHAPTER   I.     THE  OPEN  SKY 

The  Sun  — Stars  and  Planets  —  Constellations 

—  Our  Solar  Family  — The  Moon  —  Eclipses 

—  Comets 1 

Interesting  facts  about  the  heavens.    The  vast- 
ness  of  solar  distances. 


CHAPTER   II.      OUR  OWN  WORLD 

The  Size  and  Shape  of  the  Earth  —  Movements 
of  the  Earth  —  Causes  of  Seasons  —  Standard 
Time  —  International  Date  Line  —  Daylight 
Saving  —  Terrestrial  Magnetism  .  .  20 

Peculiarities  of  the  earth.  Ancient  and  medieval 
ideas. 


Following  the  chap- 
ters on  the  universe  and 
the  world,  this  chapter 
on  the  properties  and 
make-up  of  matter  an- 
swers the  question, 
"  What  is  it  all  made 
o/?" 


CHAPTER   III. 
OF  MATTER 


PROPERTIES  AND  MAKE-UP 


Forms  of  Matter  —  Properties  of  Matter  :  Ex- 
tension, Inertia,  Gravitation  —  Composition 
of  Matter  — Physical  and  Chemical  Changes  — 
Acids  —  Bases  —  Salts  —  Neutralization  .  42 

The  composition  of  water.  Iron  rust.  Uses  of 
familiar  acids,  bases,  and  salts  in  the  household. 
Manufacture  of  soap. 


VI 


CONTEXTS 


/-  This  chapter  on  the 
\  sun's  gift  of  heat  an- 
swers the  question, 
••  What  makes  it  go  ?" 
ami  deals  with  the  most 
common  form  of  en- 
ergy, heat. 


This  chapter  has  to 
do  with  air,  the  com- 
monest thing  in  our 
natural  environment. 


CHAPTER  IV.  THE  Srx's  GIFT  OF  HEAT 
Potential  and  Kinetic  Energy  —  Forms  of  En- 
ergy — ' '  Loss  of  Energy ' '  —  Conservation  of 
Energy  — Some  Elfects  of  Heat  — Mass,  Vol- 
ume, Density,  Weight  —  Nature  of  Heat  — 
Production  of  Heat  —  Combustion  —  Kindling 
Temperature  — Saving  Fuel  — Control  of  Fire 

—  Measurement    of    Temperature  —  Measure- 
ment of  Heat  —  Specific  Heat  —  Latent  Heat 

—  Transference   of   Heat :   Conduction,    Con- 
vection, Radiation  —  Conserving  Heat        .     60 
Expansion  and  contraction  of  bridge-spans,  con- 
crete   sidewalks,    table    glassware,    ice,    water, 
steam.    Use  of  kindling.    Tending  a  furnace  fire. 
Abating  the  sinoke  nuisance.    Fire  extinguishers. 
Thermometers.     Blankets    and    sheets    as    con- 
ductors   of  heat.      Heat  insulation:     revolving 
doors,  fireless  cookers,  thermos  bottles,  refriger- 
ators, and  snow. 

CHAPTER  V.  THE  ATMOSPHERE  AND  ITS 
SERVICE  TO  MAN 

Origin  of  the  Atmosphere  —  Composition  of 
Air — Need  of  Air  — Moisture  in  the  Air  — 
Evaporation  —  Boiling  —  Effect  of  Heat  on  Air 

—  Humidity  —  Humidity    and  Comfort  —  Hu- 
midity and  Health  — Weight  of  Air  — Expan- 
sion of  Air  —  Ventilation  —  Atmospheric  Pres- 
sure —  Measuring     Atmospheric     Pressure  — 
Air    Pressure    Machines  —  Air    Pressure   and 
Heat  —  Ice  Manufacture  and  Cold  Storage  — 
The  Barometer  — Determination  of  Height  by 

Air  Pressure 96 

Perspiration,    fever,   transpiration,  humidity  in 
living-rooms  and  assemblies,  humidifiers.    Circu- 
lation in  a  refrigerator,  hot-air  furnace.     Use  of 
electric  fan  in  summer  and  winter,  home-made 
ventilating  devices.    Lift-pumps.    Vacuum  clean- 
ers, street-sweeping  machines.    Compressed  air 
to  operate  air-brakes,  whistles,  ventilating  sys- 
tems, force-pumps.    Pressure  cooker.     Ice  manu- 
facture.   Cold  storage. 


CONTENTS 


Vll 


As  water  is  next  to 
air  in  importance  in 
our  environment,  its 
treatment  naturally  fol- 
lows the  chapter  on  air. 


The  chapter  on  water 
in  general  is  followed 
by  a  chapter  on  running 
water,  showing  its  geo- 
graphic and  economic 
importance. 


The  study  of  the 
chapters  on  the  earth's 
relation  to  the  sun,  and 
on  heal,  air,  and  water, 
has  paved  the  way  for 
the  introduction  of  this 
chapter  on  weather  and 
climate. 


(  1  1  A  I  TKR  VI.     THE  WATERS  OF  THE  EARTH 
Composition  of    Water  —  Effects  of   Varying 
Temperatures  on  Water  —  Ability  of  Water  to 
Absorb  Heat  —  Water  as  a  Solvent  —  Freezing 
Mixtures  —  Suspension  and  Solution  —  Emul- 
sions —  Pressure     in     Water  —  Buoyancy    of 
Water  —  Water    Reservoirs    of    the   Earth  — 
Animal  Life  in  Water  —  Waves  —  Currents  — 
Tides        .......     135 

Water,  ice,  and  steam  in  everyday  life.  Hot- 
water  bags.  Irrigation  to  prevent  freezing.  A 
"  sticky  "  salt  cellar.  Salt  on  ice  in  a  freezer,  or 
on  steps,  sidewalks,  or  car  track  switches  in 
freezing  weather.  Settling  basins,  filtration. 
Emulsifying  action  of  soap.  Pressure  in  water 
mains  and  reservoirs,  hydraulic  press.  Sub- 
marines. 


THE    WORK    OF   RUNNING 


CHAPTER   VII. 
WATER 

Power  of  Running  Water  —  River  Develop- 
ment —  Inland  Waterways  and  History  —  Sup- 
plying Water  to  Populous  Communities  — 
Pure  Water  and  Health  .  .  .  .170 
Fertility  of  "bottom-lands."  Natural  and  arti- 
ficial levees.  Harbors.  Beginnings  of  great 
cities.  Canals,  extension  of  inland  navigation. 
Ancient  and  modern  city  water  supplies,  reser- 
voirs, pumping  stations,  water  intakes.  Water 
purification,  the  St.  Louis  water  system. 

CHAPTER  VIII.  WEATHER  AND  CLIMATE 
The  Atmosphere  as  both  Blanket  and  Sun- 
Shield  —  Circulation  of  Air  —  Winds  —  Cy- 
clones and  Anti-cyclones  —  Storm-paths  — 
Sudden  Weather  Changes  —  Thunderstorms  — 
Tornadoes  —  Rainfall  —  Climate  —  Mountain: 
Seaside,  and  Island  Climates  —  Summer  and 
Winter  Resorts  .....  209 
Cold-frame.  Blizzards  and  "  hot  winds."  Fore- 
casting the  weather.  Absorption  of  heat.  Fruit- 
raising  districts. 


Vlll 


CONTENTS 


The  study  of  heat, 
air,  oxygen,  carbon  di- 
oxide, running  water, 
freezing  water,  solu- 
tions, atmospheric  mois- 
ture, evaporation,  and 
condensation  in  previ- 
ous chapters  now  en- 
ables the  pupil  to  un- 
derstand how  the  earth 
has  been  shaped  and 
how  its  rocky  surface 
was  gradually  pulver- 
ized into  soil. 


The  chapter  on  the 
origin  of  soil  is  logi- 
cally followed  by  a 
study  of  man's  use  and 
conservation  of  soils. 


Since  light  is  neces- 
sary to  life,  this  chapter 
on  light  supplements 
the  preceding  chapter 
and  prepares  for  the 
study  of  life  in  the  next 
chapter. 


CHAPTER  IX.     THE  EARTH'S  CRUST 
Changes  in  the  Earth's  Condition  —  Materials 
Composing    the  Land  — Upward   and   Down- 
ward Movements  of  the  Earth's  Crust  —  Hills 

—  Mountains  —  Plateaus  —  Plains   .         .     247 

Continental  shelf.    Newfoundland  banks.    Reefs 
and  dunes.    Buttes  and  mesas.    Erosion. 

CHAPTER  X.    PREPARATION  OF  THE  EARTH'S 
SURFACE  FOR  PLANT  LIFE 
Natural  Forces  —  Weathering  —  The  Work  of 
Wind,  Ice,  and  Snow  —  Glaciers  and  Icebergs 

—  The   Glacial    Period  —  Glacial    Formations 
and  Lakes  —  Prairies  of  the  United  States  — 
Production  of  Soils 277 

Soils  produced    by  weathering.     Ice    as  a  soil- 
builder.   Parts  of  our  country  once  covered  by  ice. 


MAN'S  USE  AND  CONSERVA- 


CHAPTER  XI. 

TIOX  OF  SOILS 

Importance  of  the  Soil  —  Composition  of  the 
Soil  — Water  Film  on  Soil  Particles  —  Fertile 
Soil  — Fertilizers  — New  Sources  of  Potash  — 
Fertilizing  Agents :  Gophers,  Moles,  Angle- 
worms, Bacteria  — Agricultural  Soils — Soil 
Water  —  Water-plants  —  Dry  Farming  —  Irri- 
gation—  Alkali  Soils  — Value  of  Soils  — Rec- 
lamation Projects  —  Forestry  .  .  .  307 

Soil  air.  Humus.  The  work  of  moles,  angle- 
worms, and  bacteria.  Sand,  silt,  and  clay. 
Drainage  and  seepage. 

CHAPTER  XII.  THE  SUN'S  GIFT  OF  LIGHT 
Light  Necessary  to  Life  —  Direction,  Intensity, 
Reflection,  and  Speed  of  Light —  Refraction 
of  Light:  Telescope,  Color  — Light  and  Com- 
fort  347 

Lenses  and  cameras.  Microscope,  telescope,  and 
spectroscope.  Light  and  health.  Natural  and 
artificial  lighting. 


CONTENTS 


IX 


Out  of  the  soil  with 
the  aid  of  light  comes 
plant  life,  on  which 
animal  life  is  ultimately 
'  dependent. 


CHAPTER  XTII.     LIFE  ON  THE  EARTH 

Plants  —  Plant  Roots — Cells — Stems  —  Graft- 
ing and  Budding  —  Leaves  —  Flowers —  Seeds 
and  Germination  —  Dependent  Plants  .  366 
Needs  of  plauts.  Functions  of  parts.  Leaves  as 
factories.  Peculiar  plants.  Pollen.  Bacteria, 
molds,  and  rusts. 

Animals  —  Invertebrates:  Protozoa,  Worms, 
Insects  —  Vertebrates  :  Man  :  Structure, 
Breathing,  Circulation,  Senses,  Sight,  Sound, 
and  Hearing,  Food  and  Digestion  .  .  399 

Health  hints.  Adenoids.  Deep  breathing.  Work 
of  white  corpuscles. 


The  treatment  of  life 
in  the  preceding  chapter 
leads  to  the  study  of 
man's  control  of  the 
means  of  maintaining 
life— food. 


CHAPTER  XIV.  MAN'S  EXISTENCE  AS  RE- 
LATED TO  PLANT  AND  ANIMAL  LIFE 

Fundamental  Foods  —  Necessary  Foods  —  Bev- 
erages —  Alcohol  —  Tobacco  —  Cooking  of 
Foods  —  Bacteria  —  Preservatives  —  Infectious 
and  Contagious  Diseases  —  Antitoxins  —  How 
to  Disinfect  —  Dangers  from  Infected  Food  and 
Water  —  Pasteurization  —  Sewage  Disposal  — 
Cleanliness  — Dangers  from  Mosquitoes,  Rats, 
Flies— Health  Hints  .  .  .  .425 

Carbohydrates,  fats,  proteins.  Minerals,  vita- 
mins, relishes.  Bacteria  in  bread,  cheese,  and 
vinegar.  Disinfection  and  sanitation. 


This  chapter  concerns 
itself  with  man's  con- 
trol of  his  physical  en- 
vironment by  means  of 
machines. 


CHAPTER  XV.  MAN'S  INVENTIONS  FOR 
TRANSFERRING  AND  TRANSFORMING  ENERGY 

Primitive  Tools  —  Friction  —  The  Lever  — 
Wheel  and  Axle  —  The  Pulley  —  The  Inclined 
Plane  — The  Wedge  —  The  Screw  —  Man's 
Most  Important  Energy  Transformers  —  Con- 
servation of  Water-power  .  .  .  459 

Work,  energy,  and  power.  Water-power,  tur- 
bines. Steam  and  gas  engines. 


CONTENTS 


Through  machines 
man  has  developed  elec- 
tricity, thus  furthering 
his  control  of  his  en- 
vironment. 


This  chapter  is  de- 
voted to  the  mysteries  of 
the  sub-surface  earth, 
following  naturally 
after  the  treatment  of 
various  aspects  of  sci- 
ence on  the  earth. 


This  final  chapter 
contains  a  general  dis- 
cussion of  the  relation 
of  life  to  physical  en- 
vironment. 


The  projects  develop 
practical  knowledge  by 
personal  investigation. 


CHAPTER  XVI.  Two  RELATED  FORCES 
THAT  MAN  HAS  HARNESSED  —  MAGNETISM  AND 
ELECTRICITY 

Magnetism  —  Magnetic  Field  of  Force  —  Mar- 
iner's Compass  —  Theory  of  Magnetism  — 
Electricity  by  Friction  —  Current  Electricity  : 
Electric  Lighting,  Electroplating  —  The  Elec- 
tromagnet :  Electric  Bell,  Telegraph,  Wireless 
Telegraph,  Telephone  —  The  Dynamo  —  The 
Electric  Motor  —  Theory  of  Electricity  .  475 

Magnets.  Dipping  needle.  Positive  and  negative 
poles.  Conductors  and  non-conductors.  Cells. 
Flatirous  and  toasters.  Welding.  Electrotyping. 
Magnetic  crane. 


WITHIN     THE     EARTH'S 


CHAPTER     XVII. 

CRUST 

Volcanoes  —  Earthquakes  —  Geysers  —  Mining 
—  The  Story  of  Coal  and  Oil  .  .  .  502 

Craters.  Lava  and  volcanic  dust.  Vesuvius  and 
Mt.  Pelee.  The  Yellowstone.  Mining  districts  of 
the  United  States. 


CHAPTER  XVIII.  LIFE  AS  RELATED  TO 
PHYSICAL  CONDITIONS 

Ancient  Life  History  —  Distribution  of  Life  — 
Effect  of  Glacial  Period  on  Plants  and  Animals 
—  Adaptability  of  Life  —  Plant  and  Animal 
Life  in  the  Sea  — Life  on  the  Land  — Distri- 
bution of  Animals  —  Life  on  Islands  —  Man 
Affected  by  Physical  Features  .  .  522 

Fossils.  Petrified  trees.  Barriers  to  distribution. 
Inland  and  seashore  life.  Strange  plants  and 
animals.  Effect  of  mountains  on  history.  Ad- 
vantages of  harbors. 


APPENDIX 
PROJECTS 
INDEX  . 


556 
563 

1 


MAPS   AND   ILLUSTRATIONS 

PAGE 

The  Climax  of  Scientific  Achievement —  Conquest  of  the  Air      Frontispiece 

Mt.  Wilson  Solar  Observatory,  the  150-foot  Tower  Telescope   .         .  1 

Surface  Explosions  on  the  Sun 3 

Sun  Spots     ............  4 

Part  of  the  Milky  Way 5 

A  Star  Cluster 6 

A  Continuous  Picture  of  the  Northern  Heavens          ....  7 

Medieval  Idea  of  the  Universe 9 

A  Large  Meteorite .12 

Mars .13 

Three  Views  of  Saturn 14 

Surface  of  the  Moon    .         .         . 14 

Phases  of  the  Moon      .         .         .         .' 15 

Total  Eclipse  of  the  Sun 16 

Halley's  Comet 17 

The  \Vorld  According  to  Hecataeus  (500  B.C.) 20 

Partial  Eclipse  of  the  Moon 22 

A  Hut  in  the  Tropics 30 

A  Laplander's  Hut 31 

Map  showing  Standard  Time  Belts      .......  34 

Map  showing  International  Date  Line 36 

Region  around  the  North  Magnetic  Pole 38 

Airplanes 45 

Three  Forces  in  Play 48 

Rusting  of  Iron 54 

Rock  Salt 55 

Kettle  Used  in  Manufacture  of  Soap 56 

A  Pile  Driver  in  Action 61 

Molten  Steel  Flowing  from  a  Blast  Furnace 69 

Tinder  Box  and  Flint  and  Steel .73 

Before  Installing  an  Underfeed  Furnace     ......  76 

After  Installing  an  Underfeed  Furnace       ......  77 

Fire  out  of  Control 78 

Revolving  Doors 91 


Xll  MAPS  AND   ILLUSTRATIONS 

PAGE 

Blue  Hill  Observatory,  Milton,  Massachusetts     .    '     .         .         .         .96 

Strato-Cumulus  Clouds 103 

Fog 105 

A  Great  Siphon  in  the  Los  Angeles  Aqueduct 119 

A  Modern  Street  Sweeper 121 

Pressure  Cooker 126 

Mercurial  Barometer 129 

Aneroid  Barometer 130 

Barograph 130 

Observation  War  Balloons 132 

Bomb  Burst  by  Freezing  Water 138 

Montezuma's  Well 140 

Settling  Basins  of  the  St.  Louis  Water  Plant 143 

A  Limestone  Cave 144 

An  American  Submarine 150 

A  Submarine  Submerging 151 

Corals 152 

"  Airing "  an  Aquarium                                    ; 153 

Mount  Everest 154 

Crinoid 155 

Ocean  Waves 158 

Fingal's  Cave 159 

A  Lake  Beach,  Formed  by  a  Stream  and  Wave  Action       .         .         .  160 

A  Sand  Spit,  Formed  by  Waves  and  Currents 161 

Ocean  Currents  of  the  WTorld       ........  163 

High  Tide  in  Nova  Scotia    .......                  .  154 

Low  Tide  at  the  Same  Place .         .  155 

Mining  Salt  in  the  Dried  up  Salton  Lake,  California  .         .         .173 

Lake  Drummond           ••-.......  174 

Gullies  Being  Cut  by  Running  Water 175 

Divides  between  Streams 176 

Niagara  Falls 177 

Stream  Working  Back  into  an  Undissected  Area        ....  178 

Yellowstone  River 179 

Platte  River 180 

River  Erosion       . 181 

Bottom  Lands 182 

Stream  Meandering  on  its  Flood  Plain 183 

Oxbow  Lakes 184 

Levee  along  Lower  Mississippi 184 

An  Old  River •  .  185 

River  Terraces,  Norway 187 

Intrenched  Meander 188 


MAPS  AND   ILLUSTRATIONS  xiii 

PAGE 

Intrenched  Meanders,  Map facing  188 

Lake  Brienz  from  above  Interlaken,  Switzerland         ....  189 

Old  Fort  Dearborn 191 

Singel  Canal,  Amsterdam .  193 

Panama  Canal 194-195 

Hot  Springs  in  the  Yellowstone  National  Park,  U.  S.  A.     .         .         .  197 

Flowing  Artesian  Well 198 

Stretch  of  a  Roman  Aqueduct  near  Nimes,  France     .         .        .        .  199 

A  Primitive  Water  Carrier  in  Mexico 200 

A  Standpipe         .         .        .        .   -    .        .        .        .        .       V        .201 

Fire-tug  in  Action .         .  •               .  202 

Wilson  Avenue  Water  Tunnel,  Chicago      .         .         ...         .  203 

One  of  the  Chicago  Intake  Cribs 204 

St.  Louis  Filter  Plant 205 

Picture  Taken  at  Midnight  on  North  Cape          . .  •     .         .         .         .  211 

Winter  Scene  in  Venice 212 

"Winter  Scene  in  Montreal   .         .         .         .         .         .                  .         .  212 

A  Sailing  Vessel  .        .        .        .....        .         .215 

Hot  Water  Tank 217 

Effect  of  Prevailing  Wind  on  Growing  Trees 218 

Wind  Map  for  January  and  February 222 

Wind  Map  for  July  and  August   .         .         .         .    .;  .         .         .         .  223 

Cyclones  and  Anti-cyclones          .         ...         .  -:    >      ..         .         .  225 

Mean  Storm  Tracks  and  Average  Daily  Movements            .         .         .  227 

A  Tornado 231 

Effects  of  a  Tornado   .        .        .        ...        ****(..,«         •         •         •  232 

Waterspout  Seen  off  the  Coast  of  New  England          ....  233 

Magnified  Snow  Crystals      ....;....  234 

Average  Rainfall  of  the  United  States 235 

Salmon  River  Dam,  Idaho 236 

Top  of  Pike's  Peak  in  Summer    .         . 239 

Popocatepetl         .        .        .        .        .\ 240 

Mid-ocean 241 

Palm  Trees  on  Tropical  Island  of  Tahiti 242 

Spiral  Nebula       .         .         .       -.        „• 247 

Folded  Strata 249 

Temple  of  Jupiter  near  Naples 250 

Old  Sea  Beaches,  San  Pedro,  California 250 

Old  Rock  Beach,  Imperial  Valley,  California 251 

Granite 253 

Fossil-bearing  Limestone     .         . 253 

Conglomerate 254 

Gneiss                                                                                                            .  255 


xiv  MAPS  AND   ILLUSTRATIONS 

PAGE 

Stratified  Rock 256 

Inland  Sea  Cave  and  Beach 258 

Coast  near  Atlantic  City 259 

A  Norway  Fiord  261 

A  Submerged  Coastal  Plain 262 

A  Norway  Fiord 263 

A  Norway  Village  at  the  Head  of  a  Fiord 264 

Lofty  Mountains 265 

The  Matterhorn 266 

The  Teton  Range,  Idaho,  U.  S.  A 267 

Colorado  Plateau 269 

The  Enchanted  Mesa,  New  Mexico     .......     270 

A  Butte .         .         .         .         .271 

An  Indian  Hogan 272 

Cliff  Dwellings,  Arizona 273 

Indian  Hieroglyphics  Cut  on  the  Steep  Wall  of  a  Mesa      .         .         .     274 

A  High,  Dry  Plain  in  Central  Nevada 274 

A  Recently  Cooled  Lava  Surface 277 

Rock  Split  by  Roots  of  Tree       . 278 

Rocks  Weathering  and  Forming  Steep  Slopes 280 

Cleopatra's  Needle,  Central  Park,  New  York 281 

Wind-Cut  Rocks,  Garden  of  the  Gods,  Colorado         .         .         .         .282 

A  Tree  Being  Dug  up  by  the  Wind 282 

A  Forest  on  Cape  Cod,  Massachusetts,  Being  Buried  in  Wind-blown 

Sand 283 

Mount  Hood,  Cascade  Range,  Oregon 286 

Snow  Fields  at  the  Head  of  a  Glacier .287 

Corner  Glacier 288 

Crevasses  in  a  Glacier 289 

The  Fiesch  Glacier .         .290 

A  Stone  Scratched  by  a  Glacier '  291 

The  Dana  Glacier  in  the  High  Sierras          .....'.     292 

A  View  of  the  Jungfrau,  Swiss  Alps 293 

An  Iceberg 294 

A  Bowlder  Borne  along  on  Top  of  a  Glacier 295 

Area  in  North  America  Covered  by  the  Ice  of  the  Glacial  Period      .     296 
Bowlders  and  Sand  Left  by  a  Retreating  Glacier         .         .         .         .298 

A  Valley  in  Norway  Rounded  out  by  Glaciers 299 

Marjelen  Lake '.300 

Alfalfa  Cutting  on  the  Fertile  Prairies          ....  .     302 

Local  Soil 308 

Relative  Sizes  of  Soil  Particles 310 

Soil  in  Good  Tilth        ...  .314 


MAPS  AND   ILLUSTRATIONS"  XV 

PAGE 

Soil  Bacteria 315 

Southern  Cotton  Field 316 

Bacterial  Nodules  on  Bean  Roots 318 

Anthill 319 

Molehills 319 

Lumpy  Soil 320 

Adobe  Soil 321 

Mud  Cracks 322 

Prairie  Scene 322 

Alfalfa  Root          .         .        .  ...        ...        .         .323 

Rice  Swamp          .         .         .        .        .        .        .        .        .        .         .324 

A  Natural  Spring 326 

An  Artesian  Spring 327 

Dry  Farming  in  Egypt 328 

Kaffir  Corn 329 

Irrigation  in  Squares    .         .         .         .         .         .         .         .         .         .     330 

Irrigation  in  Furrows   .         .         .         .         .         .  •      .    •-•  .         .         .     331 

Alkali  Soil .  •    .         .         .332 

Reclaiming  Alkali  Soil  in  the  Sahara 333 

Roman  Plowing    ...........     333 

Labor-saving  Machinery 334 

Good  Soil,  a  Truck  Farm »        .        .         .335 

East  End  of  the  Assuan  Dam  across  the  Nile 336 

Results  of  a  Sudden  Flood  .         .        .        .    .  = ;.  -      .    .     .        .         .     337 

A  Cypress  Swamp  in  Louisiana  before  Drainage         ....     337 

Cypress  Swamp  Reclaimed  .         .     •   .         .         .         .         .         .     338 

Bad  Lands  of  Dakota  .         .   '     .         '.        .        ...        .         .339 

Bad  Forestry        . 340 

Bad  Forestry        •,.'•; 341 

Bad  Forestry        .         .        •. 342 

Good  Forestry      .         .        .  343 

Good  Forestry      .         .         .         ._.'•'.'. 344 

A  Lake  Mirror     .         .         .         .         .         .  .    .     .        .         .348 

A  Reflection  Engine    .         .        .'",.' 351 

Telescope  Equipped  with  a  Spectroscope 359 

Lick  Observatory 360 

Hospital  Ward 362 

An  Old  Whale  Oil  Lamp .363 

The  Grizzly  Giant 367 

A  Typical  Plant 368 

Roots  Securely  Holding  the  Tree  Erect 369 

A  Pine  Tree 374 

A  Splendid  Tree  Developed  under  Ideal  Conditions          .         .         .     376 


XVI  MAPS  AND   ILLUSTRATIONS 

PAGE 

Banyan  Tree .377 

Different  Forms  which  Leaves  Assume 379 

A  Pine  Forest 384 

A  Sunflower  Plant 386 

Eucalyptus  Leaves 387 

Flower  showing  Different  Parts 387 

Pink  Gentian 388 

Mint  Flower 388 

Ear  of  Corn 389 

Yucca  or  Spanish  Bayonet 392 

Scrub  Oak  Branch 393 

Mistletoe  Growing  on  an  Oak 397 

Globigerina 400 

Earthworm 401 

Butterfly  on  Alfalfa 402 

Beehives 404 

A  Human  Skeleton 405 

The  Nervous  System  of  Man 406 

The  Lungs 409 

A  White  Corpuscle  Digesting  a  Germ 411 

The  Circulatory  System        . 412 

Cross  Section  of  the  Human  Heart 413 

Cross  Section  of  the  Human  Eye 414 

?Ioving  Picture  of  a  High  Jump :  415 

Cross  Section  of  the  Human  Ear 418 

Proportions  of  Elements  in  Composition  of  Living  Things          .         .  425 

A  Date  Palm         .                                   427 

A  Bunch  of  Dates 428 

Sugar  Cane  Cutting 429 

Banana  Plants 430 

Coffee  Plant 432 

Ancient  Cooking  Utensils    .         . 434 

One  Day's  Balanced  Ration  for  Five  Persons 434 

Bread  Mold 435 

Yeast  Plants         .        .         . •  .         .  436 

Bread  Making  in  Mexico 437 

Preparing  Smoked  Fish  at  Gloucester 440 

Sterilizing  Catsup  and  Chili  Sauce 441 

First  Aid  Kit 442 

Milk  Delivery  in  Belgium 446 

A  Simple  Pasteurizing  Outfit .  447 

A  Well  with  Contaminated  Water  Supply 448 

Paper  Drinking  Cup     ..........  449 


MAPS  AND   ILLUSTRATIONS  xvii 

PAGE 

Sewage  Disposal  Bed,  Solids .         .449 

Sewage  Disposal,  Liquids 450 

A  Primitive  Washing  Scene  in  Mexico 451 

A  Disease-bearing  Mosquito 452 

Amoeba  Dividing 453 

A  "  Malarial "  Swamp .453 

House  Fly .      ...        .       V       .     454 

Bacteria  Colonies          .         .         .         .         .         .  .         .         .     455 

Man's  First  War  Machine 459 

Hand  Grenade  Throwing     ...         .        .  .        .         .460 

Battle  "  Tank " *  .        .        ...     460 

Spinning  Wheel .        .         .461 

Indian  Weaving 462 

Familiar  Applications  of  the  Lever 463 

Grinding  Corn,  Scotch  Highlands .     464 

The  Lever,  as  Used  by  the  Romans  for  Weighing      ....     465 
Combination  of  Pulleys  Used  to  Lift  Heavy  Burden  ....     467 

Inclined  Railway,  Switzerland >        .         .         .     468 

Use  of  the  Wedge        .         .         .         .         .        .        .        .        .         .     469 

An  Ancient  Sail  Boat 470 

A  Simple  Water  Wheel  Used  for  Grinding  Corn        .         .         .         .471 

Electric  Power  Plant  at  Niagara 473 

A  Flash  of  Lightning .         .482 

A  Tree  Completely  Shattered  by  a  Stroke  of  Lightning     .         .         .     483 
Electric  Iron  Showing  Heating  Element     .         .         .         .         .         .     486 

Tungsten  Lamp '    .        .        .        .         .     487 

Simple  Apparatus  for  Electroplating   .         .     ,  i»        .         .         .         .     488 

An  Electrotype ' .         .         .         .489 

Electromagnetic  Crane         . 491 

Wireless  Telegraph  Station,  Los  Angeles 494 

Telephone  Station  in  the  Trenches  during  the  World  War         .         .     496 

Dynamo 497 

Power  Plant  and  Dam  of  the  Montana  Power  Company     .         .         .     498 

Electric  Locomotive 499 

San  Miguel  Harbor  in  the  Azores        . 502 

An  Hawaiian  Crater     .         .        .        .        .        .        .        .         .         .503 

Vesuvius  and  Naples    .         .         .....         .         .         .     505 

Mount  Pelee  and  the  Ruins  of  St.  Pierre 507 

Lava  Flow  in  the  Hawaiian  Islands      .......     508 

Mount  Lassen  in  Eruption 509 

The  City  of  St.  Helena 510 

Giant  Geyser  in  Eruption 511 

Fault  Line  of  an  Earthquake 513 


xviil  MAPS  AND   ILLUSTRATIONS 

PAGE 

Fence  Broken  by  the  Slipping  of  the  Earth  along  a  Fault  Line          .  514 

San  Francisco  Fire 515 

Placer  Mining  in  the  Sierras 516 

Digging  Peat  in  Ireland 517 

Coal  Mining  in  Southern  Illinois 518 

Oil  Wells 520 

Petrified  Trees 522 

Skeleton  of  an  Ancient  American  Elephant 523 

Gila  Monsters       .         .         .         . 524 

Canada  Thistle 525 

Yosemite  Falls 527 

Cacti 528 

Rattlesnake  Coiled  Ready  to  Spring 529 

A  Herd  of  Reindeer 529 

California  Rabbit  Drive 530 

Different  Kinds  of  Seaweed 531 

A  Small  Shark .532 

Flying  Fish 534 

Seals 534 

Prickly  Phlox 535 

Bird's  Nest 536 

Double  Beaver  Dam  and  Beaver  House 537 

Ostriches 538 

Opossum 538 

Kangaroo  Feeding 539 

The  Dodo     .                  540 

A  Cottage  in  the  Scotch  Highlands 541 

Cripple.  Creek 542 

A  Herd  of  Cattle  on  the  Great  Plains 544 

A  Herd  of  Bison 545 

A  Part  of  the  Plain  of  Waterloo,  Belgium 546 

Crude  Turpentine  Still 547 

Pineapples 548 

Minot's  Ledge  Lighthouse 549 

San  Francisco  Harbor,  California,  U.  S.  A 550-551 


EVERYDAY   SCIENCE 


CHAPTER  I 
THE  OPEN  SKY 


Go  forth  under  the  open  sky  and  list 
To  Nature's  teachings.  — BRYANT. 


The  Sun.  —  Our  earth  seems  so  large  to  us,  when  we 
think  of  the  time  required  for  a  trip  around  it,  that  we  meas- 
ure smaller  things  by  com- 
parison with  it.  But  the 
sun  is  so  tremendous  that 
the  earth  is  little  more 
than  a  dot  compared  with 
it.  To  make  a  trip  by 
fast  express  from  San 
Francisco  to  New  York 
requires  about  four  days, 
and  the  average  rate  of 
travel  is  about  thirty 
miles  an  hour.  If  such  a 
train  could  follow  the  line 
of  the  earth's  equator  at 
this  steady  rate,  it  could 
complete  the  circuit  of  the 

earth  in  a  little  less  than      MT.  WILSON  SOLAR  OBSERVATORY, 
.1  •   ,      r>         i  ••-,    ,     .»  150-FooT  TOWER  TELESCOPE 

thirty-five  days.      But  if     Probab]y  ^  most  effectiv 

it  were  possible   to   make  there  is  for  studying  the  sun. 

a  similar  trip  around  the  surface  of  the  sun,  more  than 
ten  years  would  be  required  for  the  journey. 


2  THE  OPEN  SKY 

To  get  an  idea  of  the  relative  sizes  of  the  earth  and  sun, 
draw  a  circle  an  eighth  of  an  inch  in  diameter  to  represent 
the  earth  and  alongside  of  it  a  circle  of  a  little  more  than 
thirteen  and  one-half  inches  in  diameter  to  represent  the  sun. 
The  diameter  of  the  earth  is  about  8000  miles,  and  the  di- 
ameter of  the  sun  is  approximately  866,000  miles.  Imagine 
that  the  sun  were  hollow  and  that  the  earth  could  be  placed 
at  the  center  of  this  hollow  sphere,  with  the  moon  just  as  far 
away  from  us  as  it  now  is  —  about  240,000  miles.  The  moon 
would  also  be  inside  the  hollow  sphere  and  almost  as  far  away 
from  its  surface  as  from  the  earth.  The  sun  is  made  up  of 
more  than  300,000  times  as  much  matter  as  there  is  in  the 
earth,  and  it  occupies  more  than  1,300,000  times  as  much 
pace. 

Astronomers  see  the  surface  of  the  sun  as  a  wild  tumult  of 
raging  flame.  The  outside  layers  are  made  up  wholly  of 
incandescent  gases ;  but  the  interior,  because  of  the  enormous 
pressure  upon  it,  must  be  in  a  molten  or  solid  condition.  Stu- 
pendous eruptions  and  tempests  of  flame  constantly  rend  its 
surface,  causing  incandescent  gases  to  shoot  up  for  hundreds 
of  thousands  of  miles.  Sometimes  furious  whirling  storms  of 
vast-diameter  occur.  These  often  continue  for  long  periods 
of  time,  and  appear  to  observers  on  the  earth  as  sun  spots. 

On  account  of  the  enormous  amount  of  heat  and  light 
given  out  by  the  sun,  it  is  well  for  us  that  the  earth  keeps 
at  an  average  distance  of  about  93,000,000  miles  from  the 
sun.  This  distance  is  so  great  that  we  can  have  no  ad- 
equate appreciation  of  it.  If  an  express  train  which  could 
travel  the  distance  of  the  earth's  circumference  in  about 
thirty-five  days,  could  start  off  into  space  and  travel  day  and 
night  at  the  same  steady  speed  in  a  straight  line  to  the  sun, 
it  would  require  more  than  350  years  to  reach  its  destination. 


THE   STARS  AT  NIGHT  3 

Of  the  total  amount  of  heat  radiated  by  the  sun,  the  earth 
receives  only  about  one  two-billionth.  Yet  this  tiny  frac- 
tion of  the  sun's  total  heat  furnishes  practically  all  the  energy 
of  the  earth.  It  has  stored  the  earth's  crust  with  coal, 
petroleum,  and  gas,  from  which  we  obtain  heat,  light,  and 
power.  It  lifts  the  waters  to  the  hills  and  covers  the  hills 
with  verdure.  It  furnishes  our  food,  the  material  for  our 


SURFACE  EXPLOSIONS  ON  THE  SUN 

These  gas  flames  shoot  thousands  of  miles  out  from  the  surface  of  the  sun. 
They  were  photographed  during  an  eclipse. 

clothing,  and  the  very  trees  that  shelter. us  from  the  mid- 
day sun. 

The  Evening  Sky.— As  the  light  of  the  sun  fades  in  the 
evening,  we  see  the  stars  coming  out  one  by  one  until  at 
last  the  sky  is  studded  with  them.  We  notice,  too,  that  the 
brighter  the  star  is,  the  sooner  it  appears.  In  the  morning 
just  the  reverse  of  this  takes  place :  the  stars  begin  gradually 
to  fade,  and  the  brightest  stars  are  the  last  to  disappear. 


4  THE   OPEN   SKY 

We  know  how  brilliant  the  light  of  a  match  appears  in  a 
dark  room,  and  how  a  light  of  this  kind  seems  to  fade  out 
when  it  is  brought  into  the  presence  of  a  strong  electric  light. 
It  would  seem  quite  probable  that  the  vast  light  of  the  sun 
might  have  the  same  effect  upon  the  light  of  the  stars.  This 
supposition  is  also  supported  by  the  fact  that  when  the  sun 
is  covered  in  an  eclipse  the  stars  begin  to  appear  as  in  the 


The  furiously  whirling  areas  shown  in  this  picture  are  thousands  of 
miles  in  diameter. 

evening.  Astronomers  all  agree  that  if  it  were  not  for  the 
greater  brilliancy  of  the  sun  we  should  see  the  heavens  full 
of  stars  all  the  tune. 

If  we  carefully  observe  these  myriads  of  bright  points 
which  dot  the  sky  at  night,  we  shall  see  that  almost  all 
of  them  shine  with  a  twinkling  light.  There  are,  how- 
ever, three  of  the  brightest  of  them  which  give  a  steady  light 
like  that  of  the  moon.  When  the  positions  of  these  three 
bodies  are  carefully  observed  for  weeks  or  months,  it  will  be 


THE   SOLAR   SYSTEM  5 

seen  that  they  are  continually  changing  their  places  among 
the  stars,  whereas  the  positions  of  the  stars  do  not  appear 
to  change  relatively  to  one  another. 

These   bright,   steady-shining   points   are   called   planets, 
from  the  Greek  word  meaning  wanderer,  and  they  belong  to 


PART  OF  THE  MILKY  WAY 

There  are  hundreds  of  millions  of  stars  in  the  Milky  Way,  so  thickly  strewn 
that  they  appear  to  the  eye  as  an  irregular  stream  of  light  across  the 
sky.  The  plate  for  this  photograph  was  exposed  ten  hours  and  a 
quarter- 

a  family  of  heavenly  bodies,  of  which  the  earth  is  one,  that 
make  regular  circuits  about  the  sun.  This  family  of  the 
sun  is  called  the  solar  system.  The  planets  are  by  far  the 
nearest  of  all  starlike  bodies,  although  the  earth's  nearest 
neighbor,  the  planet  Venus,  never  comes  nearer  than  23 
millions  of  miles.  The  most  distant  planet,  Neptune,  is 


6  THE   OPEN   SKY 

2700  millions  of  miles  farther  away  from  the  sun  than  the 
earth. 

Each  of  the  twinkling  points  in  the  heavens  is  a  sun,  shin- 
ing by  its  own  light.  Our  sun,  if  seen  from  the  distance  of 
one  of  the  nearer  stars,  would  appear  like  a  twinkling  star. 
Many  of  the  distant  stars  are  much  larger  than  our  sun. 


A  STAR  CLUSTER 
This  cluster  appears  as  a  single  star  to  the  eye. 

There  is  reason  to  believe  that  some  of  them  have  their 
families  of  planets,  and  that  our  own  solar  system  is  only 
one  of  many  similar  systems  that  exist  throughout  space. 

The  distances  to  these  suns  are  so  great,  however,  that 
their  brilliant  lights  appear  little  brighter  in  the  evening 
sky  than  the  flickers  of  so  many  candles.  The  nearest  of 
these  stars  is  probably  about  25  thousand  billion  miles 


THE  DISTANT  STARS  7 

away,  or  nearly  270,000  times  as  far  away  as  the  sun.  This 
distance  is  so  great  that  it  takes  light,  which  travels  at 
the  inconceivable  rate  of  186,000  miles  in  a  second  of  time, 


A  CONTINUOUS  PICTURE  OF  THE  NORTHERN  HEAVENS 
The  telescope  was  held  pointed  at  the  pole  of  the  heavens 
for  two  hours  and  twenty  minutes.     The  rotation  of  the 
earth  caused  the  stars  to  appear  as  white  lines,  as  if 
moving  in  circles. 

over  four  and  a  half  years  to  come  to  us  from  this  nearest 
star. 

From  Arcturus,  another  of  the  stars,  it  takes  light  about 
180  years  to  reach  us.     In  other  words,  the  light  from  Arc- 


8  THE   OPEN  SKY 

turus  which  reaches  the  eye  to-night  left  that  star  more 
than  thirty-five  years  before  the  battle  of  Lexington  and  has 
been  traveling  toward  us  ever  since  at  the  rate  of  about 
16  billion  miles  a  day.  Other  stars  are  so  much  farther 
away  that  it  is  impossible  to  measure  their  distances.  No 
wonder  the  lights  of  the  stars  are  so  dim  to  us  that  they  fade 
away  at  the  brilliant  rising  of  the  morning  sun. 

Experiment  1.  —  Early  on  a  clear  evening  when  the  stars  are 
shining  brightly  locate  the  Big  Dipper.  (See  page  10.)  Carefully 
determine  its  position  by  standing  in  a  definite  place  and  sighting 
along  the  side  of  a  high  building  or  lofty  tree.  Make  a  sketch  of 
the  position  of  the  Dipper  and  some  of  the  stars  near  it.  Several 
hours  later  in  the  evening  stand  in  the  same  place  and  determine 
in  a  similar  way  the  position.  Make  a  sketch.  Has  the  position 
of  the  Dipper  changed  in  relation  to  your  line  of  sight?  What 
caused  the  change?  Has  its  position  changed  in  relation  to  the 
other  stars?  Locate  some  other  constellations  and  make  similar 
determinations. 

All  the  stars  appear  to  be  fixed  in  their  relative  places. 
In  the  northern  hemisphere  the  stars  at  the  north  appear 
to  go  around  in  a  circle.  The  other  stars  appear  to  rise  in 
the  east  and  to  set  in  the  west  just  as  the  sun  does.  If 
we  observe  the  stars  that  rise  to  the  northeast,  east,  and 
southeast  we  shall  find  that  they  are  above  the  horizon  for 
different  lengths  of  time. 

The  ancients  noticed  these  facts  and  explained  them  by 
saying  that  the  earth  was  at  the  center  of  a  hollow  sphere, 
upon  the  inner  surface  of  which  were  the  stars,  and  that 
this  sphere  was  continually  revolving  about  the  earth, 
and  also  slightly  changing  its  position  with  respect  to  the 
earth.  We  of  the  present  day  know  that  it  is  the  earth  that 
is  turning  on  an  imaginary  axis  and  also  gradually  changing 


THE   CONSTELLATIONS 


9 


its  position  in  relation  to  the  stars.  The  points  on  the 
surface  of  the  earth  through  which  this  imaginary  axis 
passes  are  called  the  poles.  If  this  axis  were  extended  far 
enough  into  space  it  would,  at  the  present  time,  nearly 
strike  a  star  in  the  center  of  the  northern  heavens  which  we 
call  Polaris,  or  the  North  Star. 
Due  to  certain  causes,  the 
direction  of  the  earth's  axis 
slowly  changes  so  that  it  has 
not  always  pointed  so  near  to 
Polaris  as  it  now  does.  A 
writer  on  astronomy  reports 
having  visited  an  observatory 
in  China  which  was  said  to 
be  4000  years  old.  In  it  were 
placed  originally  two  bronze 
eye-holes  on  a  slanting  granite 
wall  for  the  purpose  of  sight- 
ing the  pole  star  of  that  era. 
At  the  time  of  the  astronomer's 
visit  in  1874,  the  line  of  sight 
through  these  holes  pointed  to 
a  starless  area  in  the  sky. 
Polaris  has,  however,  been  the  guiding-star  of  mariners 
for  a  thousand  years,  and  will  remain  so  for  thousands  of 
years  to  come. 

The  Constellations.  —  Probably  the  first  careful  watchers 
of  the  sky  were  the  shepherds  of  Asia.  Just  as  we  some- 
times idly  try  to  distinguish  pictures  in  the  glowing  coals 
of  a  fire,  so  they  by  stretches  of  imagination  grouped  the 
stars  into  constellations  that  very  roughly  resembled  animals 


MEDIEVAL  IDEA  OF  THE 
UNTVERSE 

From  a  fourteenth  century  manu- 
script. Above  the  earth  are  the 
clouds  and  the  moon ;  then  the 
rays  of  the  sun ;  next  the  vari- 
ous planets;  above  them  the 
stars;  and  finally  the  signs  of 
.  the  zodiac. 


10 


THE   OPEN   SKY 


with  which  they  were  familiar.  And  so  we  have  the  con- 
stellations of  the  Great  Bear,  the  Little  Bear,  the  Great 
Dog,  the  Little  Dog,  the  Bull,  the  Lion,  the  Eagle,  etc. 

The  Greeks  named  other  constellations  after  their  heroes. 
It  is  disappointing  to  see  how  little  these  star-groups  resemble 
the  objects  after  which  they  are  named,  but  we  still  retain 

the  groupings  and 
their  names  for  con- 
venience in  locating 
individual  stars. 
The  Great  Bear  and 
the  Little  Bear — 
or,  as  they  are  more 
commonly  called, 
the  Big  Dipper  and 
the  Little  Dipper  — 
are  probably  the 
best  known  of  all 
the  constellations 
because  they  are  al- 
ways in  view  in  the 

.4,  Polaris,  or  North  Star;  1,  Big  Dipper;  Band    northern        heavens. 
C,   pointers;     2,   Little    Dipper;    3,    Dragon;    ryu          .  , 

4,  Cassiopeia's  Chair;  5,  Cepheus. 

the  edge  of  the  Big 

Dipper  away  from  the  handle  are  called  the  pointers 
because  they  form  a  line  that  points  toward  the  North 
Star.  (Figure  1.) 


FIGURE  1.  —  CONSTELLATIONS  IN  THE 
NORTHERN  SKY 


Our  Solar  Family.  —  We  have  seen  that  our  mighty  sun 
and  its  family  of  planets  form  but  a  tiny  fraction  of  crea- 
tion, and  that  our  little  earth  is  comparatively  only  a  speck 
in  the  universe.  Four  of  the  eight  planets  that  revolve 


OUR  SOLAR  FAMILY 


11 


about  the  sun  are  larger  than  the  earth,  and  two  are  nearer 
to  the  sun  than  the  earth.  (Figure  2.)  The  planets  in  the 
order  of  their  distances  from  the  sun  are  Mercury,  Venus, 
Earth,  Mars,  Jupiter,  Saturn,  Uranus,  and  Neptune.  In 
the  space  between  Mars  and  Jupiter  there  has  been  found 
a  group  of  small  bodies  which  are  called  planetoids  or 
asteroids.  The  brightest  of  these  is  Vesta,  which  has  a 
diameter  of  not  more 
than  250  miles. 

"Shooting-stars  " 
(meteors)  are  small  solid 
bodies  flying  rapidly 
through  space.  Some- 
times they  enter  our  at- 
mosphere and  become 
heated  by  friction  while 
passing  through  it.  Be- 
cause they  are  thus 
heated  they  give  off  light. 
Sometimes  they  fall  to 
the  earth  as  meteorites 
but  more  frequently  they 
simply  pass  through  the  upper  part  of  the  atmosphere. 
They  are  in  no  sense  true  stars. 

Size  and  nearness  to  the  sun  are  not  the  only  respects 
in  which  the  planets  differ  from  each  other.  The  surfaces 
of  the  planets  Jupiter  and  Saturn,  for  example,  are  not  solid 
like  the  surface  of  the  earth.  Saturn  has  ten  moons  to  the 
earth's  one.  Venus  and  Mercury  have  none.  The  planet 
Mercury,  nearest  neighbor  to  the  sun,  must  receive  a  with- 
ering heat;  while  the  temperature  of  Neptune,  the  most 
distant  planet,  is  probably  colder  than  we  can  imagine. 


FIGURE   2.  —  DIAGRAM   OF  THE   SOLAR 
SYSTEM 

Showing  roughly  the  positions  of  the 
various  planets  and  their  moons. 


12 


THE   OPEN   SKY 


The  speed  of  the  planets  in  their  orbits  and  the  length  of 
their  paths  about  the  sun  vary  widely.  Mercury  travels 
through  space  about  eight  times  as  fast  as  Neptune,  and 
completes  its  comparatively  short  trip  around  the  sun  in 
about  88  days.  Neptune  requires  164  years  to  traverse 
its  vast  orbit  once. 

Astronomers  have  never  satisfactorily  determined  what 
the  length  of  day  is  on  Mercury,  Venus,  Uranus,  or  Nep- 
tune—  the  two 
planets  closest  to 
the  sun,  and  the 
two  most  distant. 
A  day  on  Mars  dif- 
fers but  little  in 
length  from  the  24- 
hour  day  of  the 
earth,  but  Jupiter 
and  Saturn  whirl 
completely  around 
on  their  axes  once 
in  about  every  ten 
hours.  The  change 
of  place  of  planets 
in  their  relations  to 
each  other  and  to 
the  stars  is  owing  to  then-  respective  motions  about  the 
sun. 

The  three  planets  which  shine  most  brightly  for  us  are 
Venus,  Jupiter,  and  Mars.  To  the  naked  eye  Venus  is  the 
most  magnificent  planet  in  the  solar  system,  exceeding  in 
light  and  beauty  the  brightest  s^ar.  It  is  therefore  called 
by  the  name  of  the  Roman  goddess  of  beauty.  Jupiter, 


A  LAHGE  METEORITE 
A  "  shooting-star  "  which  fell  to  the  earth. 


OUR  SOLAR  FAMILY 


13 


the  largest  of  the  planets  (317  times  as  heavy  as  the  earth) 
takes  its  name  from  the  king  of  the  Roman  gods.  Mars 
shines  with  a  reddish  brown  color,  and  on  this  account 
bears  the  name  of  the  Roman  god  of  war.  Saturn  is  plainly 
visible  at  times,  but  the  bright  concentric  rings,  composed 
of  little  moonlike  bodies  that  surround  it  and  revolve  about 
it,  can  be  seen  only 
with  a  telescope. 
When  once  in  about 
every  fifteen  years 
Saturn  is  so  situated 
that  we  have  a  view 
of  the  broad  side  of 
these  rings,  the  tele- 
scope reveals  what 
is  probably  the  most 
beautiful  sight  in 
the  solar  system. 
Mercury  is  so  close 
to  the  sun  that  it 
can  be  seen  by  the 
naked  eye  very 
rarely;  Uranus  can 
be  singled  out  only 
by  very  sharp  eyes;  and  Neptune  is  so  far  away  that  it 
cannot  possibly  be  seen  without  the  aid  of  a  telescope. 

The  planets  have  no  light  of  their  own,  as  do  the  true 
stars,  but  the  light  which  comes  to  us  from  them  is  a  re- 
flection of  the  light  of  the  sun.  When  the  astronomer  turns 
his  telescope  on  Neptune  and  its  moons,  he  sees  it  by  rays 
of  light  which,  in  making  the  trip  from  the  sun  to  Neptune 
and,  by  reflection,  back  to  the  earth,  have  traveled  five 


MARS 

Most  like  the  earth  of  all  the  planets.  It  is 
supposed  to  have  a  polar  ice  cap.  The  noted 
astronomer  Lowell  argues  that  Mars  may 
be  inhabited. 


14 


THE   OPEN  SKY 


THREE  VIEWS  OF  SATURN 
The  planet  with  the  beautiful  rings. 


and  a  half  billion  miles  —  the  longest  reflected  rays  of  light 
known  to  man.  If  we  could  stand  upon  any  one  of  the 
nearer  planets,  our  earth,  reflecting  the  rays  of  the  sun, 
would  also  appear  as  a  point  of  steady  light  in  the  heavens. 


SURFACE  OF  THE  MOON 
Showing  the  great  crater-like  depressions. 


THE  MOON 


15 


The  Moon.  —  We  have  learned  that  certain  of  the  planets 
are  accompanied  by  smaller  bodies  which  are  called  satel- 
lites or  moons.  These  moons  revolve  about  their  planets 
just  as  the  planets  revolve  around  the  sun.  Our  own 
moon  revolves 
around  the  earth  at 
an  average  distance 
of  about  240,000 
miles  and  makes  the 
circuit  of  its  orbit  in 
a  little  less  than  a 
month.  Primitive 
people  measured  time 
by  "  moons."  This 
is  the  origin  of  the 
word  month. 

The  moon  turns 
only  once  on  its  axis 
during  a  revolution 
around  the  earth, 
and  so  it  always 
keeps  the  same  side 
toward  us.  Its 
periods  of  daylight 
and  darkness  are, 
therefore,  about  14 
of  our  days  long. 
The  moon  has  a  diameter  of  about  2000  miles  and  its 
weight  is  about  one-eightieth  of  that  of  the  earth.  It  has 
no  air  or  water  on  its  surface.  Since  it  has  not  the  leveling 
influence  of  wind  and  rain  and  freezing  water,  the  surface 
is  very  jagged.  It  is  covered  with  great  craterlike 


PHASES  OF  THE  MOON 

Showing  roughly  the  varying  positions  of  the 
sun,  moon,  and  earth. 


16 


THE  OPEN  SKY 


depressions,  some  of  which  are  more  than   100  miles  in 
diameter. 

Although  we  see  the  moon  as  a  very  bright  object  at  night 
for  a  part  of  every  month,  yet  it  has  no  light  of  itself,  and 
all  the  light  it  gives  us  is  reflected  from  the  sun.  Astronomers 
tell  us  that  we  receive  more  heat  and  light  from  the  sun  in  a 

quarter  of  a  minute 
than  from  the  moon  in 
a  whole  year. 

As  the  earth  goes 
around  the  sun  and 
the  moon  around  the 
earth,  the  position  of 
these  three  in  relation 
to  each  other  is  con- 
stantly changing.  It  is 
profitable  to  try  to 
picture  to  oneself  the 
changing  phases  of  the 

TOTAL  ECLIPSE  OF  THE  SUN  m°°n-      Study  the  dia~ 

From  a  photograph  taken  June  8,  1918.         Sram     of      tne      moon's 

phases,   and    see    what 

the  relative  positions  of  the  sun,  earth,  and  moon  are  from 
the  new  moon  to  the  dark  of  the  moon. 

It  must  sometimes  happen  that  the  moon  comes  directly 
between  the  earth  and  the  sun.  The  moon  is  so  much 
smaller  than  the  earth,  however,  that  it  does  not  cut  off 
the  face  of  the  sun  from  the  whole  surface  of  the  earth,  but 
merely  from  a  comparatively  narrow  path.  For  hundreds 
of  miles  on  each  side  of  this  path  of  total  eclipse  of  the  sun, 
observers  see  a  partial  eclipse.  It  is  during  a  total  eclipse 
that  the  pictures  of  eruptions  of  incandescent  gases  on  the 


THE  MOON  17 

sun's  surface  are  taken.  These  form  a  corona,  or  crown  of 
light,  on  the  surface  of  the  sun  that  surrounds  the  black 
outline  of  the  moon.  It  must  also  happen  at  times  that 
the  earth  comes  between  the  moon  and  the  face  of  the  sun. 
If  the  earth's  path  lies  directly  between  the  two  bodies,  its 
shadow  wholly  obscures  the  face  of  the  moon  for  a  short 
time.  This  is  called  a  total  eclipse  of  the  moon. 


HALLEY'S  COMET 

One  of  the  most  famous  visitors  from  outer  space.     The  small  white 
dots  are  stars  seen  through  the  comet's  tail. 

If  it  were  not  for  the  moon,  the  beauty  and  variety  of 
our  nights  would  be  largely  lacking.  Moreover,  as  we  shall 
see  later,  we  should  have  no  tides  strong  enough  to  help 
vessels  over  the  bars  into  some  of  our  harbors,  and  to 
sweep  clean  our  bays,  removing  the  sewage.  If  the 
distance  of  the  moon  were  changed,  the  height  of  the 
tides  would  be  changed,  and  this  would  greatly  affect  our 
coast  towns. 


18  THE  OPEN  SKY 

Comets.  —  Sometimes  comets  appear  in  the  sky  and 
excite  the  greatest  wonder.  They  usually  have  a  very  bright 
spot  as  the  nucleus  of  a  head,  which  shades  gradually  into 
a  less  luminous  tail  that  streams  across  the  sky  for  millions 
of  miles.  Some  of  the  comets  travel  in  great  orbits  around 
the  sun  and  appear  at  regular  intervals.  They  may  be 
considered  as  part  of  the  solar  system.  Others  have  ap- 
peared once  and  then  have  disappeared,  never  to  return. 
Halley's  comet  is  probably  the  best  known  of  all  the  comets. 
It  takes  about  75  years  to  make  a  trip  around  its  orbit 
and  was  last  seen  in  1910.  It  was  named  after  the  English 
astronomer  Halley  because,  by  mathematical  calculations, 
he  traced  its  history  to  almost  the  beginning  of  the  Chris- 
tian era,  and  prophesied  correctly  the  year  of  its  next 
return. 

SUMMARY 

The  sun  is  more  than  100  times  greater  than  the  earth  in 
diameter  and  in  circumference,  and  more  than  a  million  times 
greater  in  volume.  It  appears  as  a  tremendous  ball  of  flame, 
and  is  the  source  of  the  earth's  heat  and  light. 

The  few  steady-shining  points  of  light  in  the  evening  sky 
which  are  constantly  changing  their  positions  among  the 
stars  are  planets.  These,  like  the  earth,  revolve  in  regular 
orbits  about  the  sun  as  a  center.  Each  of  the  myriads  of 
twinkling  stars  is  a  sun,  shining  by  its  own  light.  There  is 
reason  to  believe  that  many  of  these  suns  have  planets  re- 
volving about  them.  The  nearest  of  the  stars  is  thousands 
of  billions  of  miles  away,  and  the  distances  of  remote  stars 
from  the  earth  are  immeasurable.  The  ancients  thought 
that  the  earth  was  the  center  of  the  universe  and  that  the 
heavenly  bodies  revolved  about  it,  but  we  know  that  the 


QUESTIONS  19 

apparent  motions  of  the  stars  are  owing  to  the  earth's  move- 
ments on  its  axis  and  around  the  sun. 

The  ancients  grouped  the  stars  into  constellations  which 
vaguely  represented  animals  or  ancient  heroes.  Modern 
astronomers  retain  these  groupings  for  convenience  in  study- 
ing the  heavens. 

The  sun's  family  consists  of  eight  planets  and  their  satel- 
lites or  moons,  the  asteroids,  and  occasional  solar  visitors 
called  comets.  The  planets  differ  from  each  other  in  size, 
nearness  to  the  sun,  temperature,  number  of  satellites,  length 
of  orbit,  rate  of  speed,  time  of  rotation,  time  of  revolution, 
and  in  many  other  ways.  They  shine  only  by  the  reflected 
light  of  the  sun. 

All  satellites  revolve  about  the  planets  they  accompany. 
Our  own  moon  revolves  about  the  earth  at  an  average  dis- 
tance of  240,000  miles.  It  rotates  once  on  its  axis  and  travels 
once  around  the  earth  in  a  little  less  than  a  month.  The 
moon's  revolution  about  the  earth  accounts  for  its  changing 
phases,  for  eclipses  both  of  the  sun  and  of  the  moon,  and  for 
our  ocean  tides. 


QUESTIONS 

What  are  the  most  impressive  facts  about  the  sun  ? 

Why  do  we  not  see  the  stars  in  daytime? 

How  do  the  planets  differ  from  stars  ? 

Why  are  the  lights  of  the  stars  so  dim  to  us? 

Do  the  stars  appear  to  change  their  relative  positions  in  the  sky 
from  time  to  time  ?  What  makes  them  appear  to  revolve  around 
the  earth? 

In  what  respects  do  the  planets  differ  from  each  other? 

What  are  the  most  interesting  facts  about  the  moon?  What 
accounts  for  its  changes  of  appearance? 

What  causes  an  eclipse  of  the  sun?     Of  the  moon? 

What  is  a  meteorite?  a  comet?  a  constellation? 


CHAPTER     II 
OUR  OWN  WOELD 

The    Development    of    Earth-Science.  —  From    earliest 
times  men  have  earnestly  sought  to  increase  their  knowledge 


AMALCHIUM   MARE 


THE  WORLD  ACCORDING  TO  HECAT^EUS  (500  B.C.) 

about  the  earth.     The  ancient  Assyrians  and  Babylonians 

early  determined  the  definite  directions  which  we  call  north, 

20 


THE  SHAPE  OF  THE  EARTH          21 

east,  south,  and  west ;  and  carefully  built  the  sides  of  their 
temples  and  palaces  to  correspond  with  these  directions. 
The  Egyptians  developed  the  science  of  geometry  (earth- 
measuring)  primarily  for  the  purpose  of  measuring  land  areas. 
The  great  poet  Homer  shows  that  the  Greeks  of  his  time 
had  made  many  careful  observations  of  the  earth's  surface, 
as  well  as  many  ingenious  guesses  about  it.  He  conceived 
the  earth  as  a  circular  plane  surrounded  by  the  Ocean,  a 
broad  and  deep  river,  which  was  the  source  of  all  waters. 
Homer's  idea  of  the  shape  of  the  earth 
held  sway  for  hundreds  of  years.  As 
time  went  on,  however,  more  and  more 
was  learned  about  the  earth,  until  to-day 
a  great  amount  of  accurate  knowledge 
has  been  acquired,  which  is  of  the  ut-  FIGURE""!  —  DIA- 
most  value  to  mankind.  GRAM  SHOWING 

THE  SHAPE  OF  THE 
EARTH 

The  Shape  of  the  Earth.  —  Men  who  Any  drawing  which 
have  in  different  ways  made  careful  theflatteiSig^tthe 
measurements  of  the  shape  of  the  earth  poles  and  the  buig- 

,i  ,  .       .  ,,  T         -j         "MS  at  the  equator 

tell  us  that  it  is  an  oblate  spheroid  ^  Of  necessity  tre- 
(Figure  3);  that  is,  a  sphere  which  is  mendously  exagger- 
somewhat  flattened  at  two  opposite  points. 
An  ordinary  orange  has  this  shape.  The  earth  has  been  so 
little  flattened,  however,  that  its  shape  is  very  much  nearer 
that  of  a  perfect  sphere  than  is  that  of  an  orange.  Its 
polar  diameter  is  only  27  miles  shorter  than  its  equatorial 
diameter;  and  so  when  we  consider  that  each  of  its  diame- 
ters is  nearly  8000  miles,  a  shortening  of  only  27  miles  in 
one  of  these  would  not  change  its  shape  from  that  of  a 
sphere  enough  to  be  noticed  except  by  the  most  careful 
measurements. 


22 


OUR  OWN  WORLD 


Experiment  2.  —  Attach  a  centrifugal  hoop  to  a  rotator  apparatus 
and  revolve.  The  hoop  bulges  at  the  center  or  point  of  greatest 
motion  and  flattens  at  the  top  and  bottom  or  points  of  least  motion. 
The  earth  revolves  in  a  way  similar  to  the  hoop  and  is  very  slightly 
flattened  at  the  poles. 

Although  some  of  the  mountains  of  the  earth  rise  above 
sea  level  to  a  height  of  over  five  miles,  and  there  are  depths 
in  the  sea  which  are  somewhat  greater  than  this  below  sea 
level,  yet  these  distances  are  so  little  in  comparison  to  the 
size  of  the  earth  that  the  surface 
is  comparatively  less  irregular 
than  that  of  an  orange. 

In  these  days  many  men  have 
sailed  around  the  earth;  but 
valiant  indeed  was  that  little 
company  which  in  1522  first 
proved  that  it  was  possible  to 
sail  continually  in  one  direction 
and  yet  reach  the  home  port, 
thus  demonstrating  that  the  earth 
was  probably  round.  Long  be- 
fore, wise  men  had  come  to 
believe  that  the  earth  was  a  sphere,  for  it  had  been  noted 
as  far  back  as  the  time  of  Aristotle,  the  famous  Greek 
philosopher,  that  when  the  shadow  of  the  earth  fell  upon 
the  moon,  causing  an  eclipse  of  the  moon,  the  boundaries 
of  the  shadow  were  curved  lines.  It  was  also  later  noticed 
that  when  ships  are  seen  approaching  at  sea  the  masts  ap- 
pear first  and  then  gradually  the  lower  parts  of  the  ship ; 
&nd  when  ships  sail  away,  the  lower  parts  disappear  first. 

Experiment  3.  —  Add  alcohol  to  water  until  a  solution  is  obtained 
in  which  common  lubricating  oil  will  float  at  any  depth.  Insert  with 


PARTIAL  ECLIPSE  OF  THE 
MOON 

Showing  the  curved  outline 
of  the  earth's  shadow. 


THE   EARTH'S  ROTATION  23 

a  glass  tube  a  large  drop  of  oil  below  the  surface  of  the  solution.. 
The  oil  will  float  in  the  solution  in  the  shape  of  a  sphere.  This  illus- 
trates the  fact  that  if  a  liquid  is  relieved  from  the  action  of  outside 
forces,  it  will  take  the  form  of  a  perfect  sphere. 

A  spherical  surface  is  the  smallest  surface  by  which  a 
solid  can  be  bounded,  and  so  the  maximum  distance  which 
can  separate  places  located  on  a  given  solid  will  be  least 
when  its  surface  is  spherical.  Thus  the  inhabitants  of 
the  earth,  considering  the  surface  over  which  they  may 
scatter  themselves,  are  brought  into  the  closest  possible 
relation  to  one  another. 

The  Size  of  the  Earth.  —  It  is  easy  to  say  that  the  polar 
diameter  of  the  earth  is  7900  miles,  its  equatorial  diameter 

BOSTOW  TO    CHICAGO     lOQO     MILE3 


6000    MILES 


FIGURE  4.  —  LINES  TO  INDICATE  COMPARATIVE  DISTANCES 

7927  miles,  and  its  equatorial  circumference  24,902  miles, 
but  a  true  conception  of  these  distances  is  not  so  easy. 

Using  as  our  standard  any  distance  with  which  we  are 
really  acquainted,  we  shall  find  that  the  lines  representing  the 
different  dimensions  of  the  earth  are  very  long.  (Figure  4.) 
How  vastly  greater,  then,  must  be  the  distances  which  were 
mentioned  when  treating  of  the  sun  and  the  stars  ! 

The  Earth's  Rotation.  —  As  has  already  been  stated,  the 
ancients  considered  the  earth  as  the  center  of  the  universe 
and  thought  that  the  sun  and  stars  revolved  around  it. 
We  of  the  present  day,  however,  know  that  it  is  the  rotation 
of  the  earth  from  west  to  east  that  causes  the  appearance  of 
the  rising  and  setting  sun  and  thus  makes  day  and  night. 


24  OUR  OWN  WORLD 

Of  course  it  makes  no  difference  to  the  eye  whether  a 
light  is  brought  toward  the  observer  or  the  observer  goes 
toward  the  light.  We  are  turned  into  and  out  of  the 
sunlight  by  the  rotation  of  the  earth.  We  speak  of  the 
sun  as  rising  high  in  the  sky,  but  what  really  happens  is 
that  we  are  turned  so  that  the  center  of  the  earth,  our 
heads,  and  the  sun  come  nearer  and  nearer  toward  a  straight 
line. 

When  we  say  down  we  mean  toward  the  center  of  the 
earth,  and  when  we  say  up  we  mean  in  the  opposite  direc- 
tion. These  are  the  only  two  directions  that  we  could  be 
easily  sure  of,  if  it  were  not  for  the  rotation  of  the  earth. 
This  rotation  gives  the  direction  of  the  rising  sun,  which  we 
call  east,  and  of  the  setting,  which  we  call  west.  A  line  which 
runs  at  right  angles  to  the  one  joining  east  and  west,  i.e. 
one  running  parallel  to  the  axis  of  the  earth,  is  said  to  run 
north  and  south.  Thus  the  points  of  the  compass,  as  well 
as  day  and  night,  are  determined  for  us  by  the  earth's  rota- 
tion. The  north  star,  which  is  so  important  to  the  sailor 
in  determining  his  direction,  is  simply  a  star  which  is  almost 
in  line  with  the  axis  of  the  earth. 

The  rotation  of  the  earth  gives  us  also  our  means  of  measur- 
ing time. 

Days  and  Nights  of  Varying  Length. — Experiment  4.  —  (A)  In 

a  darkened  room  place  a  globe  a  short  distance  from  a  small  but  strong 
light.  Rotate  the  globe  with  its  axis  at  right  angles  to  the  line 
which  joins  the  centers  of  the  globe  and  light.  (Figure  5,  A.) 
How  much  of  the  globe  is  illuminated  by  the  light  ?  Is  the  same 
part  of  the  globe  illuminated  all  the  time  ?  Does  any  place  receive 
light  for  a  longer  time  during  a  rotation  than  any  other  place? 
Remove  the  globe  to  the  opposite  side  of  the  light  without  chang- 
ing the  direction  of  its  axis.  When  rotated,  is  there  any  change 
in  the  globe's  illumination? 


THE   EARTH'S   ROTATION 


25 


(B)  Now  make  the  axis  on  which  the  globe  rotates  parallel  to  the 
line  joining  the  centers  of  the  globe  and  light.     (Figure  5,  B.) 
Rotate  the  globe.     How  much  of  the  globe  is  illuminated  by  the 
light?     Is  the  same  part   illuminated   all  the   time?     Does  any 
place  receive  light  for  a  longer  time  during  a  rotation  than  any 
other  place  on  the  globe  ?     Remove  the  globe  to  the  opposite  side 
of  the  light  without  changing  the  direction  of  its  axis.     When 
the  globe  is  rotated,  is  there  any 

change  in  its  illumination?     If 
so,  what? 

(C)  Place  the  globe  so  that 
its   axis   is   inclined    about   25 
degrees  from  the  perpendicular 
to  the  line  joining  the  centers 
of  the  globe  and  light.     (Figure 
5,  C.)    Rotate  the  globe.    How 
much  of  it  is  illuminated?     Is 
the   same  part   illuminated  all 
the  time?     Do   any   places  in 
the    illuminated    part    receive 
light  for  a  longer  time  during 


0-1-0 


FIGURE  5. —  RELATIVE   POSITIONS  OF 
GLOBE  AND  LIGHT 

Corresponding  to  A,  B,  and  C  of 
Experiment  4. 


a  rotation  than  other  places  ? 
Remove  the  globe  to  the  op- 
posite side  of  the  light  with- 
out changing  the  direction  of 
its  axis.  When  the  globe  is 

rotated,  is  there  any  change  in  the  length  of  time  of  illumination 
of  the  places  before  noted?     If  so,  what? 

As  was  seen  in  the  previous  experiment,  the  direction  of  the 
axis  of  a  rotating  globe  has  much  to  do  with  the  light  which 
different  parts  of  it  will  receive  from  a  luminous  object. 

When  the  axis  of  the  revolving  globe  was  at  right  angles 
to  the  line  joining  the  globe  and  the  light,  no  place  on  the 
surface  of  the  globe  received  light  for  a  longer  time  than  any 
other  place.  This  was  not  true  when  the  axis  was  at  any 
other  angle. 


26  OUR  OWN  WORLD 

As  the  axis  of  the  earth  is  inclined  to  a  line  drawn  from 
the  earth  to  the  sun,  the  light  the  earth  receives  is  similar 
to  that  received  by  the  globe  in  the  last  part  of  the  experi- 
ment. Thus  the  days  and  nights  vary  in  length  during 
the  year,  because  in  summer  the  northern  hemisphere  is 
inclined  toward  the  sun  and  in  winter  away  from  it. 

The  Movement  of  the  Earth  around  the  Sun.  —  The  earth 
not  only  turns  on  its  axis  every  day,  but  it  travels  around 
the  sun,  continually  changing  its  position  in  relation  to 
the  stars.     It  moves  with  the 
tremendous   average  velocity 
of  about  19  miles  a  second. 
It    is  this  revolution  around 
the  sun  which  gives  us  our 
measure    of    time    which   we 
call    a    year.      It   takes    365 
days  and  a  fraction  to  com- 
FIGURE  6. -DRAWING  AN  ELLIPSE  P1**6  this  revolution;   and  so 
we  consider  365  days  to  be  a 

year,   and    add    a   day   practically   every   fourth   year   to 
account  for  the  fractions. 

In  the  journey  around  the  sun,  the  earth  does  not  move 
in  a  circle  but  in  an  ellipse.  To  draw  this  figure,  stick 
two  pins  into  a  piece  of  cardboard,  a  short  distance  apart. 
Place  over  the  two  pins  a  loop  of  string,  and  with  the 
point  of  a  pencil  draw  the  loop  taut  as  in  Figure  6.  If  the 
loop  is  kept  taut  as  the  pencil  point  moves  around  the  two 
pins,  the  resulting  curve  will  be  an  ellipse. 

The  points  where  the  pins  pierce  the  cardboard  are  called 
the  foci.  Draw  a  straight  line  to  join  the  foci,  and  extend 
the  line  to  cut  the  ellipse  at  two  points.  Now  place  a  small 


THE  CAUSE   OF  THE   SEASONS  27 

object  at  one  of  the  foci,  and  move  another  small  object 
around  the  ellipse.  The  two  objects  will  be  closest  together 
when  the  moving  object  reaches  one  of  the  two  points  where 

94,500,OOCLMILES 

SUMMER  WINTER 

FIGURE  7.  —  THE  EARTH'S  VARIATION  OF  DISTANCE  FROM  THE  SUN 

the  straight  line  cuts  the  curve,  and  farthest  apart  when  it 
reaches  the  other  point  of  intersection. 

Now  the  sun  is  at  one  of  the  foci  of  the  ellipse  in  which 
the  earth  moves,  and  so  the  distance  between  the  sun  and 
the  earth  varies  during  the  year.  This  variation  is  about 
three  millions  of  miles,  the  average  distance  of  the  earth 
from  the  sun  being  about  93,000,000  miles.  Strange  as  it 
may  seem,  we  are  nearest 
the  sun  in  January  and 
farthest  away  in  July. 
(Figure  7.) 


The  Cause  of  the  Sea- 
sons. —  Since  the  earth 
moves  around  the  sun 

With  its  axis  inclined  23£°.     FIGURE  8. -THE  PATH  OF  THE  EARTH 

from  the  perpendicular  to  AROUND  THE  SUN 

the  plane  of  its  Orbit,  the      Showing  roughly  the  four  positions  men- 
tioned in  the  text. 

northern  and  the  southern 

hemisphere  will  at  different  times  be  inclined  toward  and  away 
from  the  sun.  (Figure  8.)  In  July  the  earth  is  farthest  away 
from  the  sun,  but  the  northern  hemisphere  is  then  pointed 
toward  the  sun,  and  the  rays  of  heat  from  the  sun  fall  more 
nearly  vertically  upon  this  hemisphere  than  during  the  rest 


28 


OUR   OWN   WORLD 


of  the  year.  The  more  nearly  vertical  the  rays,  the  greater 
the  number  that  fall  upon  a  given  area,  and  the  greater  the 
amount  of  heat  received  by  that  area.  In  January  we 
are  closest  to  the  sun,  but  its  rays  strike  our  hemisphere 
more  aslant  and  therefore  fewer  heat  rays  fall  upon  a  given 
area  than  in  July. 

Experiment  5.  —  Cut  a  hole  4  in.  square  in  the  center  of  a  board  12 
in.  square.  Fit  tightly  into  this  hole  one  end  of  a  wooden  tube  4  in. 
square  and  1  ft.  long.  Paint  the  inside  and  outside  of  the  tube  a  dull 
black.  Hinge  the  opposite  end  of  this  tube  10  in.  from  the  end  of  a 

baseboard  2  ft.  long 
and  16  in.  wide, 
having  6  in.  of  the 
board  on  either  side 
of  the  tube.  (Fig- 
ure 9.) 

On  a  clear  day 
place  this  appara- 
tus out  of  doors  on 
a  table  freely  ex- 
posed to  the  sun, 
with  a  piece  of 

paper  on  the  baseboard  under  the  end  of  the  tube.  Point  the  tube 
directly  at  the  sun  in  the  early  morning,  in  the  middle  of  the  fore- 
noon, at  noon,  in  the  middle  of  the  afternoon  and  about  sunset. 
Mark  on  the  paper  the  amount  of  surface  illuminated  by  the  sun- 
light passing  through  the  tube  at  each  of  these  different  times.  Why 
are  different  amounts  of  surface  covered  at  these  different  times? 

Place  a  thermometer  in  the  centers  of  the  surfaces  covered  by 
the  sunlight  passing  through  the  tube  at  these  different  times.  Note 
the  different  readings  of  the  thermometer.  Can  you  suggest  a  reason 
why  they  are  not  alike  ?  The  opening  exposed  to  the  rays  has  been 
the  same  throughout  the  experiment.  Draw  diagrams  illustrating 
the  action  of  the  sun's  rays  in  the  different  positions. 

The  number  of  rays  of  the  sun  which  fall  upon  a  given 
area  depends  upon  the  angle  at  which  they  strike  the  sur- 


FIGUKE  9.  —  APPARATUS  FOR  SHOWING  THE 
HEATING  EFFECTS  OF  SUN'S  RAYS 


THE   CAUSE   OF  THE   SEASONS  29 

face.  Figure  10  shows  that  the  same  number  of  rays  fall 
upon  a  much  smaller  surface  when  the  direction  of  the  sun 
is  vertical  than  when  it  is  nearly  horizontal.  In  the  30- 
degree  arcs  there  are  2|,  7,  and  9i  ray  spaces  respectively. 
The  sun  is  here  considered  to  be  vertical  at  the  equator, 
as  it  is  on  March  21,  and  September  23.  Thus  on  these 
days,  other  conditions  being  the  same,  about  one  fourth 


FIGURE  10.  —  HEATING  EFFECTS  OF  SUN'S  RAYS 

Heating  effects  depend  upon  the  angle  at  which  the  sun's  rays  strike 
the  earth's  surface. 

as  much  heat  from  the  sun  falls  upon  the  30°  about  the 
pole  as  upon  the  30°  north  of  the  equator. 

When  the  northern  hemisphere  is  inclined  toward  the 
sun,  the  rays  of  the  sun  cover  the  north  pole  continuously 
for  six  months,  so  that  at  this  point  there  is  no  night  for  all 
that  time.  The  days  are  longer  and  the  nights  shorter 
throughout  all  the  northern  hemisphere.  More  heat  is, 
therefore,  received  in  the  northern  hemisphere  during  these 
six  months,  not  only  because  the  rays  of  the  sun  fall  more 
nearly  vertically  but  also  because  the  length  of  the  day  is 
increased. 


30  OUR  OWN  WORLD 

The  amount  of  heat  received  from  the  sun  continues  to 
increase  as  long  as  the  sun  appears  to  move  north.  The 
rays  of  the  sun  strike  vertically  the  farthest  point  north  on 
the  22d  of  June.  This  is  called  the  summer  solstice.  At 
this  time  our  days  are  the  longest  and  our  nights  are  the 
shortest.  But  the  days  are  not  the  hottest,  as  the  heat 


A  HUT  IN  THE  TROPICS 
Having  thin  walls,  but  a  heavy  thatched  roof  to  keep  out  the  rain. 

gradually  accumulates  for  some  time,  more  being  received 
each  day  than  is  given  off. 

As  the  earth  proceeds  in  its  orbit  from  this  point,  the 
inclination  of  the  north  pole  toward  the  sun  becomes  less 
and  less,  until  on  the  23d  of  September  the  sun  is  directly 
over  the  equator.  The  north  pole  now  begins  to  point 
away  from  the  sun.  On  December  22,  the  direct  rays  of 
the  sun  fall  upon  the  farthest  point  south,  our  days  being 


THE  CAUSE   OF  THE  SEASONS 


31 


then  the  shortest  and  the  days  in  the  southern  hemisphere 
the  longest.  From  this  point  until  March  21,  when  the  sun 
is  again  vertical  over  the  equator,  the  inclination  of  the  north 
pole  away  from  the  sun  decreases.  The  days  when  the 
sun  is  over  the  equator  are  called  the  autumnal  (Sept.  23) 
and  vernal  (March  21)  equinoxes,  since  the  days  and  nights 
are  then  of  equal  length  all  over  the  earth. 

The  greater  heat- 
ing of  the  hemisphere 
at  one  part  of  the 
year  than  at  another 
gives  us  the  changes 
which  we  call  the 
seasons.  Since  the 
change  in  the  length 
of  the  day  and  in  the 
direction  of  the  sun's 
rays  is  very  small 
within  the  tropics,  the 
change  in  the  amount 
of  heat  received  is 
very  slight,  so  that 
in  this  region  there 
is  almost  no  change  of  seasons.  But  at  the  poles,  where  for 
six  months  there  is  continuous  night  and  for  six  months 
continuous  day,  the  change  of  seasons  is  exceedingly  great. 
At  middle  latitudes  the  changes,  though  marked,  are  not 
excessive. 

There  are  then  two  causes  which  combine  to  give  us  our 
change  of  seasons :  the  revolution  of  the  earth  around  the 
sun,  and  the  inclination  of  the  earth's  axis  to  the  plane  of 
its  orbit. 


A  LAPLANDER'S  HUT 

Made  of  thick  sod  to  retain  heat  in 
the  frigid  zone. 


32 


OUR  OWN  WORLD 


Meridians  and  Parallels  of  Latitude.  —  For  purposes 
of  measurement,  circles  of  any  size  are  divided  into  360 
equal  parts  called  degrees.  Thus  the  equatorial  circle  of 
the  earth  is  divided  into  360  parts.  Through  each  of  these 
divisions  there  is  a  semicircle  drawn  from  pole  to  pole.  These 
semicircles  are  called  meridians.  Each  meridian  is  divided 
into  180  parts  called  degrees  of  latitude,  and  through  these 
points  of  division  are  passed  circles  parallel  to  the  equator. 
These  circles  gradually  decrease  in  size  from  25,000  miles  at 
the  equator  to  points  at  the  poles.  They  are  called  parallels 
of  latitude  and  are  numbered 
from  0  at  the  equator  to  90  at 
the  poles.  (Figure  11.) 

A  certain  one  of  the  meridians, 
usually  the  one  passing  through 
Greenwich,  England,  is  called 
the  prime  meridian  and  num- 
bered 0.  East  and  west  of  this 
the  meridians  are  numbered 
from  1  to  180.  The  degrees 
thus  numbered  are  called  degrees 
of  longitude.  Thus  we  have  a  skeleton  outline  by  means 
of  which  we  are  easily  able  to  locate  the  position  of  any 
place  upon  the  earth.  To  secure  greater  accuracy  than 
could  be  obtained  by  giving  merely  the  degrees  of  latitude 
and  longitude,  each  of  these  degrees  is  divided  into  60 
equal  parts  called  minutes,  and  each  minute  can  be  divided 
into  60  parts  called  seconds. 

The  Measurement  of  Time.  — Experiment  6.  —  On  a  fair  day 
place  a  sundial  in  an  exposed  position,  and  after  carefully  adjust- 
ing it,  compare  its  readings  with  those  of  an  accurate  watch.  Unless 
you  are  on  the  time  meridian,  the  readings  are  not  alike. 


FIGURE  11.  —  MERIDIANS  AND 
PARALLELS  OF  LATITUDE 


MERIDIANS  AND   PARALLELS   OF   LATITUDE       33 


Although  the  exact  determination  of  time  is  a  difficult 
task  and  requires  great  skill  and  very  accurate  instru- 
ments, yet  it  is  not  very  hard  to  determine  quite  satis- 
factorily the  length  of  a  solar  day.  Before  there  were  any 
clocks,  people  told  the  time  of  day  by  sundial  (Figure  12), 
which  consisted  of  a  vertical  "  pointer  "  the  shadow  of  which 
fell  upon  a  horizontal  plane.  From  local  noon,  or  the 
time  the  sun  cast  the  shortest  shadow  on  a  certain  day, 
until  it  cast  the  shortest  shadow  the  next  day,  was  con- 
sidered a  day's  time,  or 
a  solar  day,  and  was 
divided  into  twenty-four 
equal  parts  called  hours. 

The  direction  of  the 
shortest  shadow  is  a 
north  and  south  line, 
since  the  sun  must  then 
be  halfway  between  the 
eastern  and  western  ho- 
rizon. As  the  lengths  of 
these  solar  days  vary 

slightly,  for  reasons  which  cannot  be  explained  here,  we 
now  divide  the  mean  length  of  the  solar  days  for  the  year 
into  twenty-four  parts  to  get  the  hours. 

The  civil  or  conventional  day  begins  at  midnight,  not  noon. 
The  determination  of  the  exact  time  is  very  important ; 
for  the  United  States  it  is  done  at  the  Naval  Observatories 
at  Washington  and  at  Mare  Island,  San  Francisco,  and 
telegraphed  each  day  to  different  parts  of  the  country. 

Experiment  7.  —  On  a  day  when  there  appear  to  be  indications  of 
settled  fair  weather  place  a  table  covered  with  blank  paper  in  an 
open  space  where  the  sun  can  shine  upon  it.  Make  the  top  of  the 


FIGURE  12.  —  A  SUNDIAL 


34 


OUR  OWN  WORLD 


table  level  and  fix  it  firmly  so  that  it  cannot  be  moved.  Fix  ver- 
tically upon  the  table  a  knitting  needle  or  a  slender  stick.  Mark 
the  line  of  the  sun's  shadow  and  note  accurately  the  time  the 
shadow  falls  on  this  line.  On  the  next  day  note  the  time  the  shadow 
falls  upon  the  same  line.  If  your  watch  is  right,  the  difference  in 
time  it  shows  between  the  falling  of  the  shadows  the  first  and  the 
second  day  is  the  difference  between  this  particular  solar  day  and 
the  mean  solar  day.  This  may  be  nearly  a  minute.  The  shortest 
shadow  of  the  day  marks  noon.  It  extends  north  and  south. 
(Your  watch  keeps  mean  solar  time.  But  twelve  o'clock  by  your 
watch  will  probably  not  be  midday  or  high  noon,  as  your  watch 
is  set  to  Standard  Time.) 

Standard   Time.  —  When   railways   extending   east   and 
west  became  numerous  in  the   United  States   and  there 


MAP  SHOWING  STANDARD  TIME  BELTS 

were  many  through  trains  and  numerous  passengers,  it 
became  very  inconvenient  to  use  local  time,  since  no  two 
places  had  the  same  time.  Each  railway  therefore  adopted 
a  time  of  its  own,  and  when  several  railways  entered  the 


INTERNATIONAL  DATE  LINE  35 

same  city,  these  different  times  became  very  confusing. 
Therefore  in  1883  the  American  Railway  Association  per- 
suaded the  Government  to  adopt  Standard  Time. 

A  certain  meridian  was  adopted  as  the  time  meridian 
for  a  definite  belt  of  country.  The  meridians  adopted 
were  75°  for  Eastern,  90°  for  Central,  105°  for  Mountain, 
120°  for  Pacific  Time.  These  meridians  run  through  the 
centers  of  the  time  belts  and  for  7£°  on  either  side  the  time 
used  is  the  local  time  of  the  central  meridian.  When  a 
person  crosses  from  one  belt  to  another  he  finds  that  the 
time  makes  an  abrupt  change  of  an  hour.  This  system  has 
been  extended  to  all  the  United  States  possessions,  and  is 
coming  into  general  use  over  a  large  part  of  the  world. 
In  actual  practice  the  changes  of  time  are  not  made  where 
the  boundaries  of  the  time  belts  are  crossed,  but  at  im- 
portant places  near  these. 

International  Date  Line.  —  If  a  person  should  start  at 
noon  and  travel  around  the  earth  from  east  to  west  as  fast 
as  the  sun  does,  the  sun  would  be  overhead  all  the  time  and 
no  solar  day  would  pass  for  the  traveler,  even  though  24 
hours  would  be  required  for  the  trip.  But  when  he  reached 
home  he  would  find  that  a  calendar  day  had  passed.  This 
shows  the  necessity  of  having  some  generally  accepted  north 
and  south  line  on  the  earth's  circumference  from  which 
to  reckon  the  beginning  and  the  ending  of  a  day. 

Since  the  earth  rotates  once  on  its  axis  (the  full  360  de- 
grees of  its  circumference)  in  24  hours,  it  turns  in  one  hour 
^r  of  its  circumference,  or  15  degrees.  Places  on  the  earth's 
surface  that  are  15  degrees  apart  in  an  easterly- westerly  line 
may,  therefore,  be  regarded  as  an  hour  apart  in  time.  Since 
the  meridian  of  Greenwich  is  usuallv  considered  the  0  Meri- 


36 


OUR  OWN  WORLD 


dian,  let  us  suppose  it  is  high  noon  of  Sunday  at  Greenwich. 
For  every  15  degrees  west  of  that  point  it  will  be  an  hour 
earlier,  until  at  the  180th  meridian  it  will  be  midnight  of 
Saturday.  For  every  15  degrees  east  of  Greenwich  it  will 


MAP  SHOWING  INTERNATIONAL  DATE  LINE  (Dotted  line) 

In  the  northern  hemisphere,  the  Date  Line  varies  from  the  180th  meridian 
so  as  to  divide  Asia  from  North  America ;  in  the  southern  hemisphere, 
so  as  to  include  certain  English  dependencies  with  Australia  and  New 
Zealand. 

be  an  hour  later,  until  at  the  180th  meridian  it  will  be  mid- 
night of  Sunday. 

Thus,  on  one  side  of  this  line  it  would  be  Saturday  mid- 
night, and  on  the  other  side  Sunday  midnight.  This  repre- 
sents the  actual  state  of  affairs.  The  180th  meridian,  which 


MAGNETISM   OF   THE   EARTH  37 

extends  through  the  Pacific  Ocean,  is  the  accepted  line 
which  separates  one  day  from  the  next.  Thus  any  one 
traveling  around  the  earth  must  drop  a  day  from  his 
calendar  if  crossing  this  line  toward  the  west,  and  repeat  a 
calendar  day  if  crossing  the  line  toward  the  east. 

In  practice,  the  International  Date  Line,  where  this 
arbitrary  change  of  day  occurs,  does  not  quite  coincide  with 
the  180th  meridian.  A  glance  at  the  accompanying  map 
will  show  why  it  is  convenient  to  vary  the  Date  Line  from 
the  meridian  line. 

Daylight  Saving.  —  In  midsummer  the  sun  rises  between 
4  and  5  o'clock  in  middle  latitudes.  Thus  it  is  well  up  in 
the  heavens  before  the  average  citizen  is  astir.  On  the  first 
of  April,  1918,  the  United  States  Government  decided  to 
set  the  clock  ahead  one  hour.  This  gave  more  daylight  in 
the  ordinary  waking  hours,  and  thus  effected  a  saving  in 
the  cost  of  lighting.  On  the  27th  of  October,  when  the 
long  days  were  past,  the  clock  was  set  back  one  hour,  and 
normal  time  was  resumed.  Many  countries  did  this  during 
the  War. 

Magnetism  of  the  Earth.  —  There  is  a  peculiar  prop- 
erty of  the  earth  which  has  been  of  the  greatest  assistance 
to  geographical  explorers  and  without  which  it  would  be 
very  difficult  to  find  a  way  over  the  sea.  This  property 
is  called  terrestrial  magnetism.  In  very  ancient  times 
pieces  of  iron  ore  were  found  which  had  the  property  of 
attracting  iron.  Such  pieces  of  ore  are  called  loadstones. 
Artificial  loadstones  are  called  magnets. 

Experiment  8.  —  Having  pushed  a  long  cambric  needle  through 
a  small  disk  of  cork  so  that  it  will  float  horizontally,  carefully 
place  the  disk  and  needle  upon  the  quiet  surface  of  a  large  dish 


38 


OUR  OWN  WORLD 


of  water.     Does  the  needle  assume  any  definite  direction?     Taking 
the  needle  from  the  water  stroke  one  end  of  the  needle  from  the 
cork  out  with  the  north  end  of  a  magnet  and  the   opposite  end 
with  the  south  end   of  a  magnet.      When  the 
needle  is   again  floated  on  the  water  is  it  in- 
different about  the  direction  in  which  it  points? 


FIGURE  13  The  discovery  that  a  bar  of  loadstone 

or  a  magnetic  needle,  if  floated  or  freely 
suspended,  will  invariably  assume  a  definite  position  was 
made  in  the  Far  East  at  a  very  early  date,  but  it  was  put 
to  no  particular  use  in  the  sailing  of  ships  until  about  the 
middle  of  the  thirteenth  century.  Since  then  it  has 
enabled  sailors  to  go  far  out  from  the  sight  of  land  and 
yet  always  to  know  the  direction  in  which  they  are  going. 
It  was  supposed  even  up  to  the  time  of  the  first  voyage  of 
Columbus  that 
the  magnetic 
needle  always 
pointed  toward 
the  north  star  or 
perhaps  at  some 
place  a  little  to 
the  east  of  it. 
The  sailors  of 
Columbus  were 
greatly  alarmed 
when  they  found 
as  they  sailed 


REGION  AROUND  THE  NORTH  MAGNETIC  POLE 
The  +  marks  the  position  of  the  pole. 


west  that  the  needle  swung  off  to  the  west  of  the  true  north. 
This  difference  in  the  direction  of  the  needle  from  a  true 
north  and  south  line  is  called  the  declination.    The  west- 
ward declination  was  one  of  the  great  discoveries  of  Colum- 


MAGNETISM   OF  THE   EARTH  39 

bus.  We  know  now  that  the  reason  for  the  declination 
of  the  needle  is  that  the  north  end  of  it  does  not  point 
toward  the  north  geographical  pole  as  was  at  first  supposed, 
but  toward  a  point  in  the  southwestern  part  of  Boothia 
Felix  which  is  called  the  north  magnetic  pole.  The  south 
magnetic  pole  as  recently  determined  is  a  little  to  the  east 
of  Victoria  Land. 

These  magnetic  poles  do  not  remain  in  the  same  place  all 
of  the  time  but  swing  slowly  back  and  forth,  so  that  the 
declination  changes  for  the  same  place.  On  account  of 
this  it  is  necessary  for  surveyors,  who  use  the  compass,  to 
find  out  the  declination  each  year.  The  annual  change  in 
the  United  States  varies  from  0  to  5  seconds. 

SUMMARY 

The  ancients  thought  that  the  earth  was  flat ;  but  modern 
scientists  have  proved  in  many  ways  that  it  is  an  oblate  sphe- 
roid, slightly  flattened  at  the  poles  and  bulging  at  the  equator 
—  somewhat  resembling  an  orange  in  shape.  Its  polar  diam- 
eter is  7900  miles ;  its  equatorial  diameter  is  7927  miles,  and 
its  equatorial  circumference  is  24,902  miles. 

The  rotation  of  the  earth  on  its  axis  gives  us  our  days,  the 
points  of  the  compass,  and  our  means  of  measuring  time. 

The  earth  revolves  about  the  sun  once  a  year,  not  in  a 
circular,  but  in  an  elliptical,  orbit.  Its  average  distance 
from  the  sun  is  93,000,000  miles,  but  it  is  3,000,000  miles 
closer  to  the  sun  in  our  winter  than  in  our  summer.  Since 
the  axis  of  the  earth  is  inclined  23|  degrees  from  the  perpen- 
dicular to  the  plane  of  its  orbit,  the  northern  hemisphere  in 
summer  is  pointed  toward  the  sun  and  in  winter  away  from 
it.  It  is  not  closeness  to  the  sun  but  directness  of  its  ray 
that  gives  us  our  summer  heat.  The  inclination  of  the  earth 


40  OUR  OWN   WORLD 

on  its  axis  as  it  moves  around  the  sun,  therefore,  accounts  for 
our  changing  seasons.  This  inclination  also  accounts  for  the 
varying  length  of  our  days  and  nights. 

We  locate  places  on  the  earth's  surface  by  means  of  imagi- 
nary circles  drawn  around  the  earth,  which  are  called  merid- 
ians and  parallels  of  latitude.  From  the  equator  in  either 
direction  to  the  poles  is  a  quarter  of  a  circle  or  90°.  From 
a  zero  meridian  we  measure  a  half  circlet  or  180°,  east,  and 
180°  west. 

From  the  time  the  sun  casts  the  shortest  shadow  one  day 
until  it  casts  the  shortest  shadow  the  next  is  a  solar  day. 
Solar  days  differ  slightly  in  length ;  and  so,  for  convenience, 
a  calendar  day  is  the  average  of  the  solar  days  of  the  year. 
To  avoid  the  endless  confusion  that  would  be  caused  by  each 
community  having  its  own  local  time,  the  United  States  is 
divided  into  belts  15°  wide.  Throughout  one  of  these  belts, 
standard  time  is  the  same,  and  each  belt  differs  by  one  hour 
in  time  from  a  neighboring  belt.  The  International  Date 
Line  (about  the  180th  meridian)  is  the  line  which  for  con- 
venience marks  the  beginning  and  ending  of  a  calendar  day. 
Setting  the  clock  ahead  one  hour  during  the  summer  months 
gives  more  daylight  during  working  hours.  This  is  called 
daylight  saving. 

The  earth  has  a  north  and  a  south  magnetic,  pole.  These 
do  not  correspond  with  the  poles  of  the  earth's  axis,  nor  do 
they  remain  stationary.  The  attraction  of  these  poles  for 
the  magnetic  needle  or  compass  enables  mariners  always  to 
determine  direction. 

QUESTIONS 

What  simple  reasons  are  there  for  believing  that  the  earth  is 
round? 

Draw  circles  illustrative  of  the  size  of  the  earth,  moon,  and  sun. 


QUESTIONS  41 

What  was  discovered  in  the  experiment  with  the  globe  and  the 
light  ? 

How  have  the  movements  of  the  earth  around  the  sun,  its  rota- 
tion on  its  axis,  and  the  direction  of  its  axis,  affected  the  conditions 
of  your  life  ? 

Why  do  we  have  winter  in  the  northern  hemisphere  when  the 
earth  is  nearest  the  sun  ? 

If  a  man  should  leave  Cairo,  Egypt,  on  June  21  and  travel  slowly 
to  Cape  Town,  reaching  there  on  Dec.  21,  what  changes  of  season 
would  he  experience? 

How  is  the  length  of  the  day  determined?  If  it  were  noon 
Thursday,  Sept.  30,  with  you,  what  would  be  the  day  and  date  at 
Yokohama  ? 

What  are  the  advantages  of  Standard  Time?   ' 

What  are  the  reasons  for  the  establishment  of  an  International 
Date  Line? 

If  it  is  twelve  o'clock  local  time  at  your  home,  what  time  is  it  at 
Paris?  At  Honolulu? 

Why  is  the  magnetism  of  the  earth  of  so  much  use  to  man? 


CHAPTER  III 
PKOPEETIES  AND  MAKE-UP  OF  MATTEK 

Forms  of  Matter.  —  The  earth  and  the  heavenly  bodies 
are  composed  of  a  very  great  number  of  different  substances. 
With  some  of  these,  such  as  iron,  water,  air,  soil,  plants, 
etc.,  we  are  all  familiar.  These,  as  well  as  all  other  sub- 
stances, are  called  matter.  In  short,  as  scientists  say,  any- 
thing that  occupies  space  —  takes  up  room  —  is  matter. 

Matter  is  known  to  us  in  three  forms :  solids,  liquids, 
and  gases.  All  substances  exist  in  one  of  these  three  forms. 
The  forms  of  water  are  the  most  familiar  illustrations  of  this 
truth:  the  most  common  form  in  which  water  is  found  is 
liquid ;  but  as  ice  it  is  a  solid,  and  as  steam  it  is  a  gas.  Met- 
als such  as  iron,  copper,  tin,  etc.,  may  easily  be  changed 
by  heat  from  a  solid  to  a  liquid  form.  Many  metals  found 
on  the  earth  have  been  proved  to  exist  as  gases  in  the  sun. 

Properties  of  Matter.  —  Man  is  unable  to  comprehend 
how  matter  came  into  being,  or  how  it  can  ever  be  utterly 
destroyed;  but  he  does  know  many  of  the  properties  of 
matter. 

Experiment  9.  —  Pull  out  the  handle  of  a  compression  air-pump 
or  bicycle  pump.  Close  the  exit  valve  or  stop  up  the  end  of  the 
bicycle  pump.  Now  try  to  push  in  the  handle.  What  keeps  it 
from  moving  easily? 

Try  to  shove  an  inverted  drinking  glass  into  a  pail  of  water. 
(Figure  14.)     Why  does  not  the  water  fill  the  glass? 
42 


PROPERTIES   OF  MATTER 


43 


FIGURE  14 


In  the  experiment  with  the  air  compressor  we  found  that 
the  space  occupied  by  the  air  could  be  reduced  only  to  a 
iimited  extent.  Greater  force  might  have  compressed  the  air 
into  smaller  space,  but  no  amount 
of  force  could  reduce  the  air  to  a 
point  where  it  did  not  occupy  at 
least  some  space.  When  we  pump 
up  a  bicycle  tire,  we  see  again  that 
air  demands  room  for  itself.  These 
examples  illustrate  the  truth  that 
all  matter  occupies  room  or  space.  This  property  of  matter 
we  call  extension. 

Experiment  10.  —  Place  a  coin  on  a  smooth  card  extending 
slightly  beyond  the  edge  of  a  table.  (Figure  15.)  Suddenly  snap 
the  card  horizontally.  Does  the  coin  move  ? 

When  the  card  was  snapped  from  under  the  coin,  the  coin 
moved  very  slightly,  if  at  all.  The  force  of  the  finger  was 
applied  only  to  the  card,  and 
the  card  was  so  smooth  that  it 
did  not  convey  any  appreciable 
motion  to  the  coin.  If  the  coin 
had  been  glued  to  the  card,  both 
coin  and  card  would  have  moved. 
This  illustrates  the  truth  that  a  body  at  rest  does  not 
begin  to  move  unless  some  force  acts  upon  it. 

Experiment  11.  —  Revolve  around  the  hand  a  small  weight  at- 
tached to  a  strong  rubber  band.  Suddenly  let  go  the  band.  Does 
the  weight  keep  on  moving  in  the  circular  path  in  which  it  was 
revolving? 

When  we  let  go  the  band,  the  weight  started  off  in  a 
straight  line.  (Figure  16.)  It  did  not  continue  in  a  straight 


FIGURE   15 


44         PROPERTIES   AND   MAKE-UP   OF   MATTER 


FIGURE  16 


line  because  a  force  called  gravity  pulled  it  down  toward  the 
earth.  When  a  train  is  moving  along  a  straight  level  track, 
we  do  not  expect  it  to  stop  until  the  friction  of  the  track  or 
some  other  force  stops  it.  A  bullet  fired 
from  a  gun  will  continue  to  move  until 
it  hits  some  unyielding  object  or  is 
pulled  to  the  earth  by  gravity.  Thus 
we  see  that  a  moving  body  does  not  stop 
unless  some  force  compels  it  to  stop. 

We  may  sum  up  these  observations  in 
the  following  words :  A  body  at  rest 
remains  at  rest  unless  acted  upon  by  some  force;  a  body 
in  motion  continues  to  move  in  a  straight  line  at  the  same 
speed  unless  acted  upon  by  an  outside  force.  This  property 
of  matter  is  called  inertia.  Sir  Isaac 
Newton  first  stated  these  facts,  and  so 
they  are  sometimes  called  Newton's  First 
Law.  We  see  this  law  frequently  illus- 
trated when  standing  passengers  are 
jostled  off  their  feet  by  the  sudden 
starting  or  stopping  of  a  car,  or  the 
swinging  of  the  car  around  a  sharp  curve. 

Experiment  12.  —  Suspend  a  heavy  ball  by 
a  string  not  much  too  strong  to  hold  it. 
(Place  a  pad  beneath  it  to  catch  it  if  it 
drops.)  Attach  a  similar  string  to  the 
bottom  of  the  ball.  (Figure  17.)  Attempt 
to  lift  the  ball  suddenly  by  the  upper  string. 
What  happens?  Suspend  the  ball  again  and  FIGURE  17 

lift  it  very  gradually  by  the  upper  string. 
What  happens?     Now  pull  down  suddenly  on  the  lower  string. 
What  happens?     Suspend  the  ball  again  and  pull  down  gradually 
on  the  lower  string.    What  happens? 


PROPERTIES  OF  MATTER  45 

When  we  tried  suddenly  to  lift  the  suspended  ball,  the 
light  string  snapped  because  it  could  not  withstand  the 
sudden  additional  strain  of  overcoming  the  ball's  inertia. 
When  we  exerted  a  very  gradual  pull  on  the  upper  string, 


AIRPLANES 

we  overcame  the  inertia  of  the  ball  slowly  and  without  sudden 
strain  to  the  string. 

When  the  lower  string  was  suddenly  pulled,  it  broke 
because  the  ball,  through  its  inertia,  withstood  the  sudden 
effort  to  change  its  position.  But  when  the  string  attached 
to  the  bottom  of  the  ball  was  pulled  gradually,  the  upper 
string  broke.  In  this  case,  the  inertia  of  the  ball  was  over- 
come without  sudden  strain  to  the  lower  string,  and  so  this 
string  had  to  withstand  practically  nothing  but  the  pull  of 
the  hand.  The  upper  string,  on  the  other  hand,  had  to 


46        PROPERTIES  AND   MAKE-UP   OF  MATTER 

bear  the  double  strain  of  the  weight  of  the  ball  and  the 
steady  pull  of  the  hand. 

It  is  the  inertia  of  the  water  which  enables  the  small, 
rapidly  revolving  propeller  to  move  the  big  ship.  The  re- 
sistance which  the  particles  of  air  offer  to  being  thrown 
suddenly  into  motion,  their  inertia,  enables  the  propeller 
to  pull  the  airplane  along,  and  keeps  the  craft  from  falling 
to  the  ground  as  long  as  it  is  moving  rapidly.  It  is  owing 


FIGURE  18 


to  inertia  that  the  heavenly  bodies  keep  on  moving  in  space. 
Once  in  motion  they  must  keep  on  forever  unless  some  force 
stops  them. 

Experiment  13.  —  Place  a  glass  globe  partly  filled  with  water  and 
a  small  amount  of  mercury  on  a  rotating  apparatus.  (Figure  18.) 
Rotate  the  globe  rapidly.  What  do  the  water  and  mercury  tend 
to  do? 

In  Experiments  11  and  13  it  was  seen  that  revolving 
bodies  tend  to  move  away  from  the  center  around  which 
they  are  revolving.  This  is  a  manifestation  of  inertia 
which  is  sometimes  called  centrifugal  force.  The  weight 


PROPERTIES  OF  MATTER  47 

and  the  liquids  tended  to  move  away  in  a  straight  line,  but 
they  were  kept  from  it  by  the  band  and  by  the  globe. 
What  happens  when  there  is  not  sufficient  restraining  force 
is  seen  when  the  mud  flies  from  the  tires  of  a  rapidly  moving 
vehicle. 

Xewton  many  years  ago  discovered  that  all  bodies  of 
matter  have  an  attraction  for  one  another.  What  causes 
this  no  one  knows,  but  the  name  given  to  this  force  of  at- 
traction is  gravitation.  Gravitation  is  always  acting  upon  all 
bodies,  and  their  conduct  is  constantly  affected  by  it.  It 
keeps  the  heavenly  bodies  from  wandering  away  from  one 
another,  as  the  rubber  band  kept  the  weight  from  flying 
away  from  the  hand. 

Newton  also  discovered  that  the  force  of  attraction  be- 
tween two  bodies  varies  as  the  masses  of  the  bodies;  that 
is,  the  more  matter  two  bodies  contain,  the  more  they  attract 
each  other.  But  this  attraction  becomes  less  as  the  dis- 
tance between  the  bodies  increases.  The  lessening  of  the 
force  of  gravitation  on  account  of  the  increase  of  distance 
is  proportional  not  to  the  distance  but  to  the  square  of  the 
distance.  This  means  that  if  the  distance  between  two 
bodies  is  doubled,  the  attraction  between  them  is  only  one- 
fourth  as  great.  Moved  three  times  as  far  apart,  the  bodies 
have  only  one-ninth  the  attraction  for  each  other;  and  so 
on. 

When  this  attraction  is  considered  in  relation  to  the  earth 
and  bodies  near  its  surface  the  term  gravity  is  used.  We  are 
constantly  measuring  the  pull  of  gravity  and  calling  it 
weight.  It  is  the  force  which  causes  us  to  lie  down  when  we 
wish  to  sleep  comfortably,  and  which  makes  all  unsupported 
bodies  fall  to  the  earth. 

If  two  forces  act  upon  a  body  free  to  move,  each  will  in- 


48         PROPERTIES   AND   MAKE-UP   OF   MATTER 


fluence  the  direction  of  its  motion,  and  it  will  go  in  the 
direction  of  neither  force  but  in  a  direction  between  the  two. 
If  there  are  more  than  two  forces,  the  path  of  the  object 
acted  upon  will  be  the  result  of  the  action  of  all  the  forces. 
In  the  case  of  the  weight  and  the  rubber  band  we  found 
that  the  moving  weight  when  not  held  by  the  force  of 
the  band  flew  away  from  the  hand.  The  rubber  band  con- 
tinually pulled  in  toward  the  hand,  while  owing  to  inertia 
the  weight  tended  to  go  off  in  a  straight  line.  The  result 

, ,     was     that     the     weight 

neither  went  in  toward 
the  hand  nor  off  in  a 
straight  line,  but  in  a 
curved  path. 

Planetary  Movements. 
—  We  have  seen  that 
the  sun  is  the  great 


THREE  FORCES  IN  PLAT 
See  the  accompanying  diagram. 


FIGURE  19 


center  around  which  the  earth  and  the  other  members  of  the 
solar  system  revolve.  The  mass  of  the  sun  is  so  great  that 
the  attraction  of  gravitation  between  it  and  the  planets  holds 
these  with  their  satellites  in  their  paths  and  keeps  them  from 
flying  off  into  space.  In  fact  the  laws  of  inertia  and  gravita- 
tion explain  the  entire  mode  of  action  of  the  heavenly  bodies. 


COMPOSITION   OF  MATTER  49 

So  thoroughly  have  mathematicians  mastered  these  un- 
varying laws  that  they  can  tell  just  where  in  their  orbits 
the  earth  or  any  of  the  planets  will  be  at  any  future  time, 
or  were  at  any  past  time.  The  exact  date  of  any  eclipse 
in  the  future  or  in  the  past  can  be  determined,  and  even  the 
path  of  the  moon's  shadow  across  the  earth.  Disputed 
dates  of  events  in  ancient  history  which  occurred  during 
eclipses  of  the  moon  have  been  determined  to  the  exact 
hour  in  this  way. 

One  hundred  years  ago  Uranus  was  thought  to  be  the 
farthest  planet  in  the  solar  system.  But  years  of  patient 
observation  revealed  the  fact  that  its  movement  was  not 
in  exact  accord  with  the  schedule  astronomers  had  mapped 
out  for  it.  Two  mathematicians,  one  in  France  and  the 
other  in  England,  working  separately  without  each  other's 
knowledge,  concluded  that  this  must  be  owing  to  the  at- 
traction of  a  more  distant  planet,  as  yet  undiscovered.  They 
calculated  what  must  be  the  exact  position  of  this  planet. 
When  on  the  night  of  September  23,  1846,  a  telescope  was 
directed  to  this  point,  a  half  hour's  search  revealed  the 
planet  Neptune. 

Composition  of  Matter.  —  It  is  the  work  of  chemists  to 
find  out  of  what  matter  is  composed.  They  tell  us  that  all 
matter  consists  of  minute  particles,  called  molecules.  These 
molecules  are  constantly  moving  about  in  the  spaces  that 
exist  between  them,  hitting  and  bumping  against  one 
another. 

The  fact  that  minute  invisible  particles  may  be  given  off  by 
a  substance  is  readily  shown  by  opening  a  bottle  of  ammonia 
or  exposing  a  piece  of  musk  in  a  room.  Soon  in  every  part 
of  the  room  the  presence  of  these  substances  may  be  recog- 


50         PROPERTIES   AND   MAKE-UP   OF   MATTER 

nized  by  the  odor.     Yet  nothing  can  in  any  possible  way  be 
seen  to  have  been  added  to  the  air. 

Experiment  14.  —  Dip  a  glass  rod  in  strong  hydrochloric  acid 
and  hold  it  a  few  inches  above  the  open  mouth  of  a  bottle  of  strong 
ammonia  water.  Nothing  can  be  seen  to  be  emitted  from  either 
the  rod  or  the  bottle,  but  when  they  are  brought  near  together  a 
cloud  of  little  white  particles  is  formed.  This  must  be  due  to  the 
action  of  an  invisible  something  which  came  from  the  ammonia 
upon  an  invisible  something  which  came 
from  the  hydrochloric  acid,  resulting  in  the 
formation  of  something  that  is  visible. 

Molecules  are  too  small  to  be  seen 
by  the  most  powerful  microscope. 
There  are  millions  of  them  in  a  par- 
ticle of  matter  as  big  as  the  head  of  a 
pin.  Some  one  has  said  that  if  a  drop 
FIGURE  20  °f  water  could  be  magnified  to  the  size 

of    the    earth,   the    molecules    would 
probably  appear  no  larger  than  a  baseball. 

It  has  been  found  possible  by  chemical  and  electrical 
means  to  divide  molecules  into  smaller  particles  called 
atoms,  and  very  recently  to  find  out  something  about  the 
composition  of  the  atoms  themselves.  For  example,  the 
smallest  particle  in  which  water  can  exist  and  still  be  water 
is  a  molecule.  By  means  of  an  electric  current  these  mole- 
cules can  be  broken  up.  But  when  we  thus  divide  the 
molecules  of  water  we  no  longer  have  water;  we  have  two 
gases,  hydrogen  and  oxygen. 

Experiment  15.  —  (Teacher's  Experiment).  —  Procure  from  the 
chemical  laboratory  an  electrolysis  apparatus  or  arrange  an  ap- 
paratus as  shown  in  Figure  21.  This  consists  of  a  glass  dish  partly 
filled  with  water  to  which  a  little  sulphuric  acid  has  been  added. 
(The  sulphuric  acid  is  needed  only  to  aid  in  carrying  the  electricity 


COMPOSITION   OF  MATTER 


51 


between  the  platinum  foils.)  Two  copper  wires  each  having  a 
small  piece  of  platinum  foil  attached  to  one  end  are  so  arranged  that 
the  platinum  foils  extend  up  vertically  in  the  water. 

Fill  two  test  tubes  with  the  water  in  the  dish  and  invert  them 
over  the  platinum  foils.  To  the  ends  of  the  copper  wires  attach 
a  battery  consisting  of  several  dry  cells.  Bubbles  of  gas  will 
begin  to  rise  in  the  test  tubes  as  soon  as  the  battery  is  connected. 
One  of  the  tubes  will  fill  twjce  as  fast  as  the  other.  When  this 
tube  is  full  quickly  invert  it  and  apply  a  lighted  match  to  its  mouth. 


FIGURE  21 

There  will  be  a  sharp  explosion.  This  gas  is  hydrogen.  Invert 
the  other  tube  and  insert  a  splinter  with  a  glowing  spark  at  its 
end.  The  spark  will  burst  into  flame.  This  gas  is  oxygen. 

Chemists  have  learned  that  every  molecule  of  water 
contains  two  particles  of  hydrogen  and  one  particle  of  oxy- 
gen. These  particles  are  called  atoms.  An  atom  of  hydro- 
gen is  hydrogen ;  an  atom  of  oxygen  is  oxygen  —  no  other 
substance.  For  that  reason,  hydrogen  and  oxygen  are 
known  as  simple  substances  and  are  called  elements.  But 
since  the  smallest  particle  of  water  —  a  molecule  —  is  com- 
posed of  hydrogen  and  oxygen,  water  is  not  a  simple  sub- 
stance but  a  compound  of  two  other  substances.  Chemists 
therefore  call  water  a  compound. 

Every  kind  of  matter  known  to  man  is  classified  as  either 
an  element  or  a  compound.  So  far  there  have  been  dis- 
covered only  about  eighty  elements  —  eighty  substances  that 
cannot  be  reduced  to  simpler  substances.  Among  these  are 


52         PROPERTIES   AND   MAKE-UP   OF   MATTER 

iron,  copper,  tin,  aluminum,  lead,  zinc,  mercury,  gold, 
silver,  nickel.  The  gases  hydrogen,  oxygen,  and  nitrogen 
are  also  elements. 

Most  substances  are  compounds.  The  number  of  com- 
pounds as  compared  with  the  number  of  elements  in  nature 
may  be  illustrated  in  this  rough  way.  There  are  only  26 
letters  in  the  English  alphabet,  but  these  may  be  combined 
in  so  many  different  ways  that  we  have  thousands  of  English 
words.  Just  so  there  are  to  our  knowledge  only  about 
eighty  different  elements  in  the  world.  But  these  elements 
unite  in  so  many  different  ways  and  in  so  many  different 
proportions  that  we  have  innumerable  compounds. 

But  the  comparison  of  letters  and  words  with  elements 
and  compounds  must  go  no  farther  than  to  show  how  many 
more  compounds  there  are  than  elements.  The  eye  can 
pick  out  all  the  different  letters  that  compose  every  word. 
But  when  the  atoms  of  different  kinds  of  elements  combine 
into  molecules,  the  resulting  compound  substance  is  so 
different  from  the  elements  composing  it  that  there  is  no 
apparent  relationship. 

Water  furnishes  a  good  illustration.  Oxygen  is  a  gas 
that  must  be  present  wherever  there  is  burning.  Hy- 
drogen burns  very  readily  in  the  presence  of  oxygen.  But 
water,  every  molecule  of  which  is  made  up  of  atoms  of  these 
two  gases  and  is  the  result  of  the  burning  of  hydrogen  in 
oxygen,  is  our  main  dependence  for  putting  out  fires. 

Physical  and  Chemical  Changes.  Experiment  16.  —  Mix  a 
little  powdered  sulphur  with  about  half  as  much  powdered  iron  or 
very  fine  iron  filings.  Examine  the  mixture  with  a  magnifying  glass. 
You  can  easily  distinguish  between  the  particles  of  iron  and  sulphur. 
Put  the  mixture  into  a  test  tube  and  heat  it  over  a  Bunsen  burner. 
(Figure  22.)  The  mixture  will  glow  and  become  a  solid  mass. 


PHYSICAL  AND  CHEMICAL  CHANGES  53 

Break  the  test  tube  and  examine  the  solid  with  a  magnifying  glass. 
Can  you  now  distinguish  the  iron  from  the  sulphur?  The  solid  is  a 
chemical  compound  called  iron  sulphide.  , 

When  water  freezes  it  does  not  become  a  different  sub- 
stance ;  it  is  still  water,  but  water  in  a  solid  state.  When 
water  is  "  boiled  away  "  or  evaporated  by  the  heat  of  the 
sun,  it  is  still  water,  but  water  in  a  gaseous  state.  When 
the  iron  used  in  Experiment  16  was  pulverized  it  still  re- 
mained iron.  Such  changes  as  these,  which  do  not  affect  the 
nature  of  a  substance,  are  called  physical 
changes.  •  •  «  .  * 

But  when  molecules  break  up  into 
their  atoms,  or  atoms  unite  to  form 
molecules,  a  chemical  change  is  said  to 
occur.  Such  is  the  change  that  occurs 
when  hydrogen  and  oxygen  unite  to 
form  water ;  or  when  the  electrical  cur-  FIQU 

rent  breaks  up  the  molecules  of  water 
into  the  two  kinds  of  atoms  composing   them;    or  when 
sufficient  heat  is  applied  to  an  iron  and  sulphur  mixture. 

One  of  the  most  common  examples  of  chemical  change 
is  the  rusting  of  iron  exposed  to  air.  The  atoms  of  oxygen 
in  the  air  and  in  the  water  of  the  air  combine  with  the  iron 
to  produce  rust.  A  chemical  change  takes  place  and  a 
compound  of  the  two  elements  is  formed  which  is  entirely 
different  in  its  nature  from  either. 

A  chemical  compound  such  as  iron  rust,  made  up  of  oxygen 
and  some  other  element,  is  called  an  oxide. 

Mixtures  must  be  carefully  distinguished  from  chemical 
compounds.  If  we  mix  milk  and  water,  neither  the  water 
nor  the  milk  is  really  changed  in  nature  as  the  result  of  put- 
ting them  together  in  the  same  vessel.  If  we  try  to  mix 


54         PROPERTIES   AND   MAKE-UP   OF   MATTER 

oil  and  water  their  failure  to  combine  into  a  third  substance 
is  even  more  noticeable.  After  a  little  while  the  water  will 
be  found  at  the  bottom  of  the  vessel  and  the  oil,  which  is 
lighter,  will  float  on  top.  A  chemical  compound  is  very 
different  from  such  mixtures,  as  we 
learned  in  the  case  of  water  and  of 
iron  sulphide. 

Acids,  Bases,  and  Salts.  The 
most  important  chemical  compounds 
for  us  to  consider  are  acids,  bases, 
and  salts.  Acids  of  various  kinds 
exist  in  apples,  grapes,  rhubarb, 
buttermilk,  vinegar,  lemons,  oranges, 
and  other  familiar  substances. 

A   small   amount   of    very   dilute 

RUSTING  OF  IRON          hydrochloric  acid  is  formed  in  the 
stomach  of  man  and  of  some  other 

animals  and  helps  in  the  process  of  digestion.  Hydrochloric 
acid,  sulphuric  acid,  and  nitric  acid  are  much  used  in  the 
laboratories  and  in  various  industries. 

Many  acids  are  liquid;  and  dilute  solutions  (little  acid 
in  much  water)  of  all  common  acids  taste  sour.  Acids 
turn  blue  litmus  paper  to  red.  Litmus  paper  is  paper  which 
has  been  especially  prepared  by  treating  it  with  a  vegetable 
substance  called  litmus,  obtained  from  a  low  order  of  plants 
called  lichens.  Strong  acids  may  cause  great  injury  to 
cloth,  paper,  wood,  or  the  flesh  of  animals. 

It  is  important  that  we  should  become  acquainted  with 
another  class  of  compounds  called  bases  that  are  in  some 
ways  just  the  opposites  of  acids.  Most  bases  are  in  the 
form  of  solids ;  and  dilute  solutions  of  almost  all  the  bases 


ACIDS,   BASES,   AND   SALTS 


55 


taste  bitter.  Litmus  paper  that  has  been  turned  red  by 
acids  will  be  changed  back  to  blue  by  a  base.  Some  of  the 
most  common  bases  of  the  household  are  ammonia  water, 
baking  soda,  limewater,  caustic  potash  (lye),  and  caustic 
soda.  Certain  strong  bases  are  usually  called  alkalies. 
Caustic  potash  and  caustic  soda  are  two  of  the  commonest 
and  strongest  alkalies. 

Experiment  17.  —  Into  a  clean  test  tube  containing  pure  water 
put  a  small  piece  of  blue  litmus  paper.  Pour  into  the  test  tube  a 
little  hydrochloric  acid.  What  happens  to  the  litmus  paper? 
Now  add  a  solution  of  caustic  soda,  drop  by  drop,  until  the  litmus 
paper  takes  on  a  pale 
bluish  red  shade.  Taste 
a  drop  of  the  solution  in 
the  test  tube.  The  test 
tube  will  be  found  to 
contain  water  with  com- 
mon salt  dissolved  hi  it. 
By  evaporating  the 
water,  crystals  of  salt 
may  be  obtained. 

This  process  of  com- 
bining an  acid  and  a  ROCK  SALT 
base  in  right  propor- 
tions, by  which  a  substance  is  produced  that  is  neither 
an  acid  nor  a  base,  is  called  neutralization.  The  result  of 
such  a  chemical  combination  is  water  and  a  salt.  There 
are  many  different  kinds  of  salts;  but  the  salt  with 
which  we  are  most  familiar  is  sodium  chloride,  or 
common  table  salt,  which  resulted  from  the  preceding 
experiment. 

Strong    acids    and    bases    will    corrode    metals,    discolor 
clothing,  or  even  "  eat  "  holes  in  it,  and  cause  ugly  flesh 


56 


PROPERTIES   AND   MAKE-UP   OF   MATTER 


I 


wounds.  But 
neutral  substances 
will  do  none  of 
these  things. 

A  strong  base 
like  lye  is  just  as 
dangerous  to 
handle  as  a  power- 
ful acid.  It  is 
well  to  bear  in 
mind  then  that 
bases  and  acids 
counteract  or 
neutralize  the  de- 
structive effects 
of  each  other.  If 
lye  is  spilled  on 
the  hands  or 
clothing,  vinegar 
or  lemon  juice 
should  immedi- 
ately be  applied 
to  neutralize  the 
base.  If  acid  is 
spilled,  ammonia 
water  is  the  safest 
base  to  counter- 
act it  since  it  will 
do  the  least  harm 

Courtesy  of  The  Procter  and  Gamble  Company  if  tOO  much  is  USed . 

KETTLE  USED  IN  MANUFACTURE  OF  SOAP  E  very  house  wife 
This  kettle  is  16  feet  in  diameter,  three  stories  high, 

and  it  holds  about  375,000  pounds  of  soap.  knOWS     that     am- 


ACIDS,   BASES,   AND   SALTS  57 

monia  water  may  be  used  in  a  number  of  different  ways  to 
help  remove  grease  from  various  kinds  of  fabrics,  and  that 
lye  will  act  upon  grease  in  such  a  way  that  water  will  dis- 
solve it.  Lye  is  therefore  used  for  "  cutting  "  the  grease 
in  drain  pipes  leading  from  sinks.  But  since  lye  and  other 
strong  bases  which  "  cut "  grease  will  also  ruin  most  fabrics 
and  will  do  harm  to  the  skin,  a  milder  cleansing  agent  must 
be  found  for  laundry  and  personal  use.  Soap  is  one  of 
those  substances  which  chemists  call  salts,  and  is  made  by 
mixing  or  boiling  fats  with  lye. 

The  neutralizing  of  acids  by  means  of  some  mild  base  is 
a  part  of  the  daily  experience  of  many  people,  even  though 
they  may  not  realize  what  the  chemical  action  is.  We  put 
ammonia  or  damp  baking  soda  on  a  bee-sting  to  neutralize 
the  acid  that  the  bee  has  injected  into  the  flesh.  Baking 
soda  is  used  by  housewives  to  sweeten  sour  milk.  Frugal 
cooks  sprinkle  baking  soda  lightly  over  rhubarb,  gooseberry, 
or  cherry  pie  in  order  partly  to  neutralize  the  acids  and 
thus  to  save  sugar. 

The  farmer  uses  lime  to  "  sweeten  "a  "  sour  "  or  acid 
soil.  Physicians  often  prescribe  limewater  or  a  solution  of 
baking  soda  to  neutralize  acidity  (sourness)  of  the  stomach. 
Fruit  stains  are  caused  by  fruit  acids.  For  that  reason, 
the  stains  may  usually  be  removed  by  soaking  the  linen  in  a 
weak  solution  of  ammonia  or  borax. 

The  wonderful  progress  that  man  has  made  in  the  last 
century  in  manufacturing,  transportation,  agriculture,  build- 
ing, sanitation,  and  comfortable  living  conditions,  has  come 
out  of  his  greatly  increased  scientific  knowledge,  and  out 
of  his  increasing  ability  to  control  forms  of  energy  which 
produce  desired  chemical  and  physical  changes. 


58        PROPERTIES  AND   MAKE-UP   OF  MATTER 


SUMMARY 

Anything  that  occupies  space  is  matter.  Matter  is  known 
to  us  in  three  forms  —  solids,  liquids,  and  gases.  Matter 
has  certain  properties,  such  as  extension,  inertia,  and  gravi- 
tation. The  laws  of  inertia  and  gravitation  explain  so  per- 
fectly the  movements  of  the  heavenly  bodies  that  their 
courses  may  be  accurately  foretold. 

All  matter  consists  of  particles  called  molecules,  too  small 
to  be  seen  with  the  most  powerful  microscope.  Molecules 
may  be  divided  into  smaller  particles  called  atoms.  If  the 
molecules  of  a  substance  may  be  broken  up  into  two  or  more 
kinds  of  atoms,  the  substance  is  called  a  compound ;  if  not, 
it  is  called  an  element.  There  are  about  eighty  elements 
known  to  scientists.  All  other  substances  are  compounds. 

When  molecules  of  a  substance  gain  atoms,  lose  atoms,  or 
exchange  atoms  with  molecules  of  other  substances,  a  chem- 
ical change  is  said  to  occur.  Any  other  kind  of  change  in 
matter  is  a  physical  change.  If  when  we  combine  two  sub- 
stances, the  molecules  remain  unchanged,  we  have  a  mixture ; 
if  atoms  of  different  kinds  unite  into  molecules,  we  have  a 
chemical  compound. 

Acids,  bases,  and  salts  are  most  important  chemical  com- 
pounds. Acids  exist  in  many  familiar  substances.  Many 
acids  are  liquid.  Dilute  solutions  of  common  acids  taste 
sour.  Acids  turn  blue  litmus  paper  red.  Bases  are  in  some 
ways  just  the  opposite  of  acids.  Most  bases  are  solid  and 
dilute  solutions  of  them  taste  bitter.  They  turn  red  litmus 
paper  blue. 

Strong  acids  and  bases  are  injurious  to  flesh  or  to  common 
substances.  The  process  of  combining  an  acid  and  a  base  is 
called  neutralization,  and  the  result  is  water  and  a  salt.  A 


QUESTIONS  59 

salt  has  none  of  the  caustic  or  corroding  properties  of  bases 
and  acids.  Using  some  base  to  neutralize  an  acid  is  a  com- 
mon household  experience.  Strong  bases  like  lye  are  used  to 
"  cut "  grease  from  wood  or  metal.  For  milder  cleansing 
purposes  we  use  soap,  which  is  neither  an  acid  or  a  base, 
but  a  salt. 

QUESTIONS 

In  what  three  forms  does  matter  exist? 

Name  and  illustrate  three  universal  properties  of  matter. 

What  daily  experiences  of  yours  are  explained  by  these  three 
properties? 

Why  does  a  motorman  slow  up  his  car  at  a  sharp  curve? 

What  keeps  the  planets  moving  around  the  sun  and  in  their 
orbits? 

Of  what  do  chemists  regard  all  substances  to  be  composed? 
Why? 

What  is  the  difference  between  a  physical  and  a  chemical  change? 
Give  an  example  of  each. 

In  what  respects  do  acids,  bases,  and  salts  differ  from  one  another? 
Illustrate. 

For  what  purpose  have  you  ever  used  an  acid,  a  base,  or  a  salt  ? 


CHAPTER  IV 
THE  SUN'S  GIFT  OF  HEAT 

The  sun  is  not  only  the  ruler  of  the  solar  system  in  that 
it  holds  the  planets  in  their  orbits  as  they  revolve  about  it ; 
it  also  controls  the  activities  upon  the  planets  since  it  fur- 
nishes them  with  their  heat  and  light.  Without  the  heat 
of  the  sun  the  earth  would  be  a  cold,  barren,  lifeless,  inert 
ball  of  matter  and  nothing  more.  The  sun's  gift  of  heat  is 
all  important. 

Everybody  has  observed  many  of  the  effects  of  heat.  It 
melts  ice.  It  converts  water  into  steam.  It  cooks  food. 
Thus  we  see  that  heat  has  the  ability  to  cause  change.  The 
capacity  for  causing  change,  for  overcoming  resistance,  for 
doing  work,  is  called  energy.  Heat  is  therefore  a  form  of 
energy. 

A  body  may  have  through  its  position  or  its  composition 
the  ability  to  do  work  without  actually  being  at  work.  It 
is  then  said  to  have  potential  energy.  The  moment  a  body 
begins  to  do  work,  its  energy  is  called  kinetic  energy.  Either 
kind  of  energy  may  be  transformed  into  the  other. 

A  brick  on  a  chimney  top  has  potential  energy  owing  to 
its  position.  If  some  force  pushes  it  off,  its  potential  energy 
is  transformed  into  kinetic  energy.  When  you  wind  a 
clock,  the  energy  you  expend  is  transmitted  to  the  spring, 
and  the  spring  is  wound  into  such  a  position  that  it  possesses 
potential  energy.  Thus  your  kinetic  energy  is  stored  up 
60 


POTENTIAL  AND   KINETIC   ENERGY 


61 


in  the  spring  as  potential  energy.  Slowly  the  change  of 
position  of  the  spring  transforms  its  potential  energy  back 
into  kinetic  energy. 

When  a  gun  is  loaded  with  powder  it  has  potential  energy 
due  to  the  composi- 
tion of  the  powder. 
When  the  powder  is 
exploded,  the  poten- 
tial energy  changes 
into  kinetic  energy 
which  is  imparted  to 
the  bullet.  The 
smallest  possible 
amount  of  nitroglyc- 
erine has  potential 
energy  on  account  of 
the  arrangement  of 
the  atoms  in  its  mol- 
ecules. When  that 
arrangement  is  dis- 
turbed, potential 
energy  becomes  ki- 
netic and  an  explosion 
results. 

The  sun  through- 
out its  existence  has 
been  sending  vast 
quantities  of  energy 
to  the  earth.  This 
energy  has  been 
mostly  in  the  forms 


of    heat    and    light. 


Courtety  of  Illinois  Central  Railroad 
A  PILE  DRIVER  IN  ACTION 

The  weight  or  "  ram  "  is  lifted  to  the  top  of 
the  machine,  where  it  has  great  potential 
energy.  As  it  falls,  it  changes  its  potential 
energy  into  kinetic  energy  and  drives  the 
pile. 


62  THE    SUN'S   GIFT    OF   HEAT 

The  ability  of  the  earth  to  support  plant  or  animal  life  or 
to  furnish  man  the  power  necessary  to  carry  on  his  industries 
is  due  to  the  energy  furnished  by  the  sun.  Plants  cannot 
grow  without  the  energy  furnished  by  the  sunlight,  and 
animals  could  not  live  were  it  not  for  the  energy  furnished 
them  by  the  plants. 

We  often  think  that  there  are  many  different  sources  of 
energy  such  as  waterpower,  wood,  coal,  oil,  and  others ;  but 
when  these  are  traced  back,  their  energy  is  found  to  have 
come  from  one  source,  the  sun.  The  water  which  the  sun 
has  evaporated  and  carried  by  cloud  and  shower  to  the 
mountain  lake  is  stored  there  and  has  potential  energy.  It 
is  ready  to  run  down  the  valleys  changing  its  potential 
energy  into  kinetic  and  doing  work.  Without  the  heat  of 
the  sun  there  would  be  no  life  upon  the  earth,  no  flowing 
streams,  no  changing  winds,  none  of  the  restless  energy 
which  makes  the  world  as  we  know  it. 

For  untold  ages  plants  utilized  the  sun's  energy  and  stored 
it  up.  It  was  preserved  in  the  remains  of  plants  in  the  form 
of  coal.  This  coal  is  now  being  burned  to  furnish  power  to 
carry  on  man's  industries.  Thus  nature  has  run  a  savings 
bank.  The  sun's  kinetic  energy  was  transformed  and  stored 
for  ages  in  the  earth's  vaults  as  potential  energy,  and  now 
issues  from  the  burning  coal  as  kinetic  energy  to  do  our 
bidding. 

The  motion  of  the  falling  brick  was  a  manifestation  of 
energy  due  to  gravitation.  The  explosion  of  the  gunpowder 
was  due  to  chemical  energy.  The  ordinary  street  car  runs 
by  virtue  of  electrical  energy.  Thus  we  see  that  there  are 
other  forms  of  energy  besides  heat  and  light.  But  one  form 
of  energy  may  be  readily  changed  into  another  form,  as 
when  the  steam  engine  transforms  the  energy  in  coal  into 


CONSERVATION   OF   ENERGY 


63 


mechanical  energy,  or  when  this  mechanical  energy  is  changed 
by  the  dynamo  into  electrical  energy.     (Figure  23.) 

If  you  have  ever  bored  a  hole  in  hard  wood,  you  have 
noticed  how  hot  the  point  of  the  drill  becomes.  A  portion 
of  the  energy  you  expended  went  to  displace  the  particles 
of  wood,  and  a  portion  of  your  energy  was  transformed 
by  friction  into  heat.  The  portion  of  your  energy  which  was 
transformed  into  heat  is  usually  referred  to  as  lost  energy, 
because  it  did  not  help  to  accomplish  the  work  you  set  out 


FIGURE  23.  —  TRANSFORMATION  OF  ENERGY 

to  do.  Whenever  man  undertakes  to  change  one  form  of 
energy  into  another,  there  is  always  this  "  loss  of  energy." 

In  a  factory,  for  example,  a  great  deal  of  the  heat  from 
the  burning  fuel  goes  up  the  chimney  and  is  also  lost  in 
other  ways.  Even  that  part  of  the  heat  which  is  transformed 
into  mechanical  energy  cannot  all  be  utilized.  Much  of  it 
is  transformed  back  into. heat  by  the  friction  of  the  moving 
parts  of  the  machinery. 

In  reality,  however,  no  energy  is  ever  lost  or  destroyed. 
It  may  be  lost  in  the  sense  that  it  does  not  serve  man's 
immediate  purpose,  but  it  has  not  gone  out  of  existence. 
The  same  thing  may  be  said  of  energy  that  was  said  of 


64 


THE    SUN'S   GIFT    OF   HEAT 


matter.  Man  can  neither  create  it  nor  destroy  it.  He 
may  only  transform  it.  This  great  truth  has  been  deter- 
mined by  a  vast  amount  of  most  careful  investigation,  and 
is  called  the  law  of  conservation  of  energy. 

Some  Effects  of  Heat.  —  The  following  experiments  illus- 
trate a  common  effect  of  heat. 

Heat.  —  Experiment  18.  —  Fit  a  glass  flask  with  a  one-hole  rubber 
stopper  through  which  passes  a  glass  tube  about  20  cm.  long. 
Place  this  on  a  ringstand  so  that  the  end  of  the 
tube  extends  down  into  a  bottle  nearly  filled  with 
water.  (Figure  24.)  Gently  heat  the  flask.  The 
air  expands  and  bubbles  rise  in  the  water.  When 
the  flask  cools,  the  air  contracts  and  water  rises  in 
the  tube. 

Experiment  19.  —  Fill  the  flask  used  in  the  last 
experiment  with  colored  water.     See  that  the  end 
of    the    glass   tube    passing   through    the    rubber 
stopper  is  just  even  with  the  bottom  of  the  stopper. 
Smear  the  lower  part  of  the  stopper  with  vaseline 
and  insert  it  in  the  flask,  being  careful  that  the 
flask  and  a  few  centimeters  of  the  tube  are  filled 
with  the  colored  water  and  that  there  are  no  air 
bubbles  in  the  flask.     Mark,  by  slipping  over  a 
rubber  band,  the  end  of  the  water 
column  in  the  tube.     (Figure  25.) 
Heat  the  flask.    The  water  expands. 
Experiment  20.  — Pass  the  ball 
of  a  ball-and-ring  apparatus  through 
the  ring.    (Figure  26.)     Notice  how 
closely  it  fits.     Heat  the  ball  in  a 
Bunsen  flame  for  several  minutes. 
See   if    the   ball   will  now  go  through  the   ring. 
Explain  why  it  does  not. 


FIGURE  24 


FIGURE  25 


FIGURE  26 


We  saw  in  these  experiments  that  heat  caused  the  gas, 
the  liquid,  and  the  solid  to  expand.     Cooling  had  the  reverse 


SOME   EFFECTS   OF  HEAT  65 

effect.  On  every  hand  expansion  and  contraction  due  to 
changes  in  temperature  must  be  taken  into  account.  The 
ends  of  steam  pipes  are  allowed  to  be  free  and  are  never 
attached  firmly.  The  ends  of  the  spans  of  long  iron  bridges 
are  placed  on  rollers.  In  places  where  there  are  considerable 
ranges  of  temperature  concrete  sidewalks  are  cut  into  squares 
instead  of  being  laid  as  continuous  solid  surfaces.  When 
iron  tires  are  fitted  to  wagon  wheels  they  are  first  heated 
and  then  placed  on  the  wheels  and  allowed  to  cool.  Tele- 
phone wires  are  tighter  in  winter  than 
in  summer.  For  this  reason  they  are  not 
stretched  taut  when  put  up. 

Experiment  21.  —  Heat  a  metal  compound  FIGURE  27 

bar.     It  bends  over  on  one  side.     The  more 
the  bar  is  heated  the  more  it  bends.     (Figure  27.)     The  two 
metals  do  not  expand  at  the  same  rate. 

Various  solids  and  liquids  expand  and  contract  at  different 
rates.  Platinum  expands  and  contracts  at  almost  the  same 
rate  as  glass.  When  platinum  and  glass  are  fused  together 
they  expand  and  contract  almost  as  one  substance.  For 
this  reason,  in  the  manufacture  of  incandescent  lamps,  plati- 
num is  the  only  substance  that  can  be  used  to  pass  through 
glass  to  carry  the  electrical  current  to  the  filament  within. 
Other  metals  contract  either  more  rapidly  than  the  glass 
and  thus  let  air  into  the  bulb,  or  more  slowly  and  thus 
break  the  glass.  One  reason  why  mercury  is  used  in  ther- 
mometers is  that  it  changes  rapidly  in  volume  with  changes 
in  temperature. 

Different  parts  of  the  same  substance  will  expand  at 
different  rates  according  to  the  amount  of  heat  applied. 
When  experienced  housewives  wash  glasses  in  hot  water, 
they  do  not  dip  them  slowly ;  they  plunge  them  in  quickly 


66  THE   SUN'S   GIFT   OF   HEAT 

so  as  to  allow  them  to  expand  at  the  same  rate  throughout 
and  thus  to  prevent  their  breaking.  This  explains  why  it 
is  unwise  to  pour  boiling  water  slowly  in*o  a  cold  glass,  or 
cold  water  slowly  into  a  hot  glass. 

The  experiment  with  the  ball-and-ring  apparatus  easily 
makes  clear  the  meaning  of  the  terms  mass,  volume,  density, 
and  weight,  which  we  shall  have  occasion  to  use  from  time 
to  time.  After  the  iron  ball  was  heated,  it  contained  no 
more  iron  than  before  it  was  heated.  The  amount  of  matter 
in  it,  its  mass,  remained  the  same.  But  under  heat  the  iron 
expanded  and  occupied  more  space;  that  is,  its  volume 
was  greater.  Heat  increased  the  volume, 
but  not  the  mass,  of  each  of  the  sub- 


CORK 


stances  we  experimented  upon. 


— .        We  all  know  that  some  substances  are 
^j    heavier  than  others.     A  cubic  inch  of 
FIGURE    28.  — EQUAL   lead,   for  example,   is   heavier   than   a 

MASSES     OF     CORK    cubic    inch    of    CQrk       We  that    the 

AND  LEAD  * 

lead  has  greater  density  than  the  cork ; 
that  is,  a  piece  of  lead  has  more  matter  in  it  than  a  piece  of 
cork  of  the  same  volume.  (Figure  28.) 

Weight  is  simply  the  measure  of  attraction  between  the 
earth  and  the  body  weighed.  The  greater  the  amount 
of  matter,  the  greater  is  the  attraction  between  it  and  the 
earth;  that  is,  the  greater  its  weight.  Weight,  however, 
must  not  be  confused  with  density.  The  farther  away  a 
substance  is  from  the  center  of  the  earth,  the  less  it  weighs. 
(Page  47.)  A  cubic  inch  of  lead  would  weigh  appreciably 
less  at  the  top  of  a  high  mountain  than  at  the  level  of  the 
sea.  But  the  density  of  the  lead  would  not  be  affected  by 
its  distance  from  the  earth's  center. 

When  the  iron  ball  was  heated,  its  volume  was  increased, 


NATURE  OF  HEAT  67 

Its  density  was  decreased,  but  its  mass  remained  the  same. 
Since  the  mass  remained  the  same  as  before  heating,  and  its 
distance  from  the  earth's  center  was  unchanged,  it  weighed 
the  same  as  before. 

When  heat  was  first  studied  it  was  thought  to  be  an 
invisible  fluid  without  weight  which  worked  itself  into 
bodies  and  caused  them  to  expand  in  the  same  way  that 
water  affects  a  sponge  or  a  piece  of  wood.  This  fluid  was 
supposed  to  be  driven  out  by  pounding  or  rubbing.  Even 
the  primitive  savages  knew  that  fire  could  be  obtained  by 
rubbing  two  dry  sticks  together. 

About  the  close  of  the  eighteenth  century  an  American, 
Count  Rumford,  who  was  boring  some  cannon  for  the 
Bavarian  government,  showed  that  the  amount  of  heat 
developed  seemed  to  be  entirely  dependent  upon  the  amount 
of  grinding  or  mechanical  energy  expended.  The  old  theory 
of  a  fluid  prevailed,  however,  until  about  the  middle  of  the 
nineteenth  century,  when  a  great  English  experimenter 
by  the  name  of  Joule  showed  conclusively  that  the  amount 
of  heat  developed  was  due  entirely  to  the  amount  of  energy 
which  apparently  disappeared  into  the  heated  body. 

We  learned  in  Chapter  III  that  all  matter  consists  of 
constantly  moving  particles,  or  molecules,  with  spaces  be- 
tween them.  WThen  a  substance  is  heated  the  molecules 
move  more  rapidly  and  strike  each  other  harder.  This 
drives  the  molecules  farther  apart  and  causes  the  substance 
to  expand.  Heat  is  a  form  of  energy  which  manifests  itself 
in  the  motion  of  these  molecules  of  matter.  If  a  condition 
could  be  reached  where  there  was  no  molecular  motion,  there 
would  be  no  heat. 

If  we  apply  sufficient  heat  to  ice,  the  molecules  hit  against 
one  another  so  rapidly  and  so  hard  that  the  ice  loses  its  defi- 


68  THE    SUN'S   GIFT    OF   HEAT 

nite  shape  and  melts  down  into  water.  If  now  we  apply  suffi- 
cient heat  to  the  water,  the  motion  of  the  molecules  becomes 
so  violent  that  they  fly  off  from  one  another  in  steam.  But 
while  this  effect  of  heat  in  changing  ice  to  water  and  water  to 
steam  is  familiar  to  us  all,  it  is  not  so  generally  known  that 
the  application  of  sufficient  heat  will  change  other  substances 
from  a  solid  to  a  liquid  and  from  a  liquid  to  a  gaseous  state. 

Iron,  for  instance,  may  be  solid  as  we  ordinarily  see  it, 
or  liquid  as  it  comes  from  the  blast  furnace,  or  gas  as  it 
exists  in  the  indescribably  hot  atmosphere  of  the  sun. 
When  heat  is  withdrawn,  the  processes  are  reversed,  from 
gas  to  liquid  and  then  to  solid. 

Some  substances,  such  as  camphor,  pass  from  a  solid  state 
directly  to  a  gaseous  state.  Even  ice  may  do  this  under 
certain  conditions.  Housewives  in  cold  climates  know, 
for  example,  that  clothes  on  the  line  will  "  freeze  dry  " 
in  zero  weather. 

Substances  usually  expand  as  they  change  from  the  solid 
state  to  the  liquid  state,  and  contract  when  the  process  is 
reversed.  Ice  is  a  notable  exception  to  this  general  rule, 
since  when  water  freezes  its  volume  increases.  If  it  were 
not  for  this,  ice  would  not  float.  Certain  metals  such  as 
cast  iron  also  have  the  property  of  expanding  at  the  moment 
of  solidifying.  Type  metal  is  a  mixture  of  metals  that 
possesses  this  property.  It  is  poured  into  the  molds  in 
a  molten  condition.  When  it  solidifies  it  expands  and 
forces  itself  into  every  available  crevice,  thus  taking  on 
the  sharp  outlines  that  type  must  have. 

Substances  always  increase  in  volume  as  they  change 
from  a  liquid  to  a  gaseous  state.  Engineers  roughly  esti- 
mate, for  example,  that  a  cubic  inch  of  water  makes  a 
cubic  foot  of  steam. 


PRODUCTION  OF  HEAT 


69 


Courtesy  of  American  Steel  Foundrie* 
MOLTEN  STEEL  FLOWING  FROM  A  BLAST  FURNACE 

.    The  liquid  steel  is  here  conducted  by  a  duplex  spout  into  two  20-ton 
ladles,  ready  for  casting  in  the  molds. 

Production  of  Heat.  —  Heat  may  be  produced  in  several 
different  ways,  but  the  most  common  way  is  by  burning. 
Our  houses  are  usually  heated  by  burning  wood  or  coal. 
If  we  wish  the  fire  in  the  stove  to  burn  more  brightly  we 
open  the  draft;  if  more  slowly,  we  close  it.  Apparently 


70 


THE    SUN'S   GIFT    OF   HEAT 


the  supply  of  air  has  much  to  do  with  the  fierceness  of 
the  fire. 

Experiment  22.  —  Wind  a  short  piece  of  wire  around  a  small 
piece  of  candle  and  after  lighting  the  candle  lower  it  into  a  wide- 
mouthed  bottle.      Insert  a  stopper  into  the 
mouth  of  the  bottle.     The  candle  will  begin 
to  smoke  and  will  soon  go  out. 

From  the  foregoing  experiment  it 
appears  that  a  supply  of  .air  is  necessary 
for  the  burning  of  the  candle.  Experi- 
ence shows  that  this  is  true  in  all  the 
forms  of  combustion  familiar  to  us. 


Experiment  23.  —  (Teacher's  Experiment.) 
—  Obtain  four  bottles  of  oxygen  from  the 
chemical  laboratory.  If  not  obtainable,  place 
a  piece  of  sodium  peroxide  (oxone)  about  as 
large  as  the  end  of  a  finger  in  a  side-necked 
test  tube  provided  with  a  medicine  dropper 
filled  with  water,  as  shown  in  Figure  29.  Put 
the  end  of  the  delivery  tube  under  the  mouth 
of  an  inverted  bottle  filled  with  water  arranged 
on  the  shelf  of  a  pneumatic  trough.  Drop 
FIGURE  29  water  slowly  on  to  the  sodium  peroxide  and 

collect  the  gas  generated.  Fill  several  bottles. 

Oxygen  can  also  be  prepared  by  heating  a  mixture  of  about  one 

part  manganese  dioxide  and  two  parts  potassium  chlorate  in  a 

test  tube  and  collecting  the  gas  over  water.     (Figure  30.)     Does 

the   appearance   of  this 

gas  differ   hi   any  way 

from  air?     Smell  of  it. 

Has  it  any  odor?    Into 

one    of   the    bottles    of 

oxygen  insert  a  splinter 

of  wood  having  a  spark 

at  the  end.      It   bursts  FIGURE  30 


COMBUSTION  71 

into  flame.     Does  the  same  thing  take  place  when  the  stick  with 
the  spark  upon  it  is  held  in  a  bottle  of  air? 

Hold  a  lighted  match  at  the  mouth  of  another  of  the  bottles 
containing  oxygen.  Does -the  gas  itself  burn  as  illuminating  gas 
does  when  a  match  is  applied  to  it  ?  If  the  oxygen  in  the  air  were 
increased  or  decreased,  it  would  have  a  great  effect  upon  combus- 
tion. Attach  a  piece  of  sulphur  to  a  short  piece  of  picture  wire. 
Ignite  it  and  place  the  wire  in  a  bottle  of  oxygen. 
(Figure  31.)  Does  the  sulphur  burn  strongly? 
How  about  the  wire?  Does  it  burn  too? 

In  the  experiment  just  performed,  we  found 
that  substances  burn  in  oxygen  much  more 
fiercely    than   in   air,   and   that    substances        FIGURE  31 
which  do  not  burn  in  air  readily  burn  in 
oxygen.     Experiments  have  shown  that  oxygen,  a  gas  which 
is  in  the   air  about  us,   must    be  present  where  burning 
occurs.     In  fact  burning  is  the  result  of  the  chemical  union 
of  atoms  of  oxygen  with  atoms  of  other  substances. 

The  paraffin  in  the  candle  is  a  compound  that  contains 
both  hydrogen  and  carbon.  These  two  elements  are  found 
in  all  common  fuels  and  are  sometimes  called  fuel  elements. 
Both  of  them  readily  unite  under  proper  conditions  with 
oxygen,  and  the  chemical  action  produces  heat.  When 
wood  or  coal  burns,  the  atoms  of  the  fuel  elements  in  these 
substances  unite  with  atoms  of  oxygen. 

Experiment  24.  —  (Teacher's  Experiment.)  —  Put  a  few  zinc 
scraps  in  a  test  tube  and  pour  a  little  hydrochloric  acid  upon  them. 
Feel  the  test  tube  near  the  zinc. 

Put  half  an  inch  of  water  into  another  test  tube  and  carefully 
pour  a  little  strong  sulphuric  acid  down  the  sides  of  the  tube  into 
the  water.  Feel  the  tube. 

Burning  is  not  the  only  way  in  which  chemical  action 
produces  heat.  In  the  preceding  experiments,  both  test 


72  THE    SUN'S   GIFT    OF   HEAT 

tubes  were  found  to  have  been  heated  by  the  chemical  ac- 
tion which  took  place,  but  no  combustion  occurred. 

But  chemical  action  is  only  one  of  the  sources  of  heat. 
Every  Boy  Scout  is  taught  to  make  a  fire  by  rubbing  two 
pieces  of  dry  wood  together. 
(Figure  32.)  He  knows  that 
friction  is  a  method  of  produc- 
ing heat;  or  to  state  it  another 
way,  the  mechanical  energy  of 
rubbing  is  transformed  into  heat 

FIGURE  32. -BOY  SCOUT  OUT-  energy.     We  shall  find  in  Experi- 
FIT  FOR  MAKING  FIRE 

ment   157    that  electrical    energy 

can  be  changed  into  heat  energy.  The  change  of  chemical, 
mechanical,  and  electrical  energy  into  heat  energy  are  the 
three  ways  in  which  we  produce  heat. 

Kindling  Temperature.  —  We  have  found  by  experience 
that  a  certain  amount  of  heat  is  necessary  to  get  things  to 
burn.  Two  sticks  have  to  be  rubbed  until  they  are  very 
hot  before  they  take  fire.  We  use  kindling  to  get  large 
pieces  of  wood  and  coal  hot  enough  to  burn.  Everything 
has  to  be  brought  to  a  certain  temperature  before  it  will 
take  fire.  This  temperature  is  called  the  kindling  tempera- 
ture. 

The  kindling  temperatures  of  different  substances  vary 
greatly.  The  kindling  temperature  of  phosphorus  is  a 
little  below  the  temperature  of  the  human  body,  and  phos- 
phorus is  therefore  a  dangerous  thing  to  handle.  The 
kindling  temperature  of  iron  is  many  hundreds  of  degrees. 

Certain  substances  very  readily  unite  with  the  oxygen  of 
the  air  at  ordinary  temperatures  and,  by  so  doing,  of  course 
produce  heat.  If  the  heat  thus  produced  does  not  escape, 


KIXDLIXG   TEMPERATURE 


73 


the  substances  will  in  time  be  raised  to  their  kindling  tem- 
perature and  will  take  fire.  This  is  called  spontaneous  com- 
bustion. 

Linseed  oil  used  by  painters  is  a  substance  which  readily 
oxidizes.  Accumulations  of  rags  saturated  with  such  oil 
will  gather  heat  of  oxidation  (if  in  a  place  where  there  is 
no  great  movement  of  air)  until  the  kindling  temperature 
is  reached,  and  a  fire  is  started.  Sometimes  the  dust  in 
the  center  of  a  great  pile  of  coal  produces  heat  enough  by 
its  oxidation  to 
start  a  fire  in  the 
coal.  Some- 
times the  heat 
produced  by  the 
"  souring  "  of 
hay  is  sufficient 
to  set  the  hay 
on  fire. 

A  means  by 
which  substances 
can  be  readily 
brought  to  their  kindling  temperature  is  very  essential  if 
fires  are  to  be  easily  built.  Our  forefathers  used  to  strike 
a  flint  and  steel  together  so  as  to  make  a  spark  fall  upon 
some  fine,  dry  material  (tinder).  With  this  they  patiently 
started  the  larger  fires  they  needed. 

In  frontier  days,  smoldering  tinder  was  kept  in  a  "  tinder 
box,"  and  this  served  the  pioneers  instead  of  matches. 
Until  less  than  a  hundred  years  ago  the  use  of  flint  and  steel 
was  the  prevailing  method  of  obtaining  fire. 

This  method  of  starting  fire  was  difficult  and  uncertain. 
The  invention  of  the  friction  match  has  changed  all  this  and 


TINDER  Box  AND  FLINT  AND  STEEL 


74  THE    SUN'S   GIFT   OF   HEAT 

made  the  production  of  fire  easy  and  certain.  It  has  been 
one  of  the  great  factors  in  making  life  comfortable.  The 
earlier  matches  consisted  of  a  splinter  of  wood  tipped  with 
a  mixture  of  sulphur,  yellow  phosphorus,  potassium  chlorate 
or  red  lead,  held  together  by  glue.  When  struck  on  a  rough 
surface  the  heat  of  friction  was  sufficient  to  ignite  the  phos- 
phorus, thus  causing  the  other  materials  to  burn  and  the 
splinter  of  wood  to  catch  fire. 

It  was  soon  found  that  the  use  of  ordinary  phosphorus 
was 'very  dangerous  to  the  matchmakers,  causing  a  dread- 
ful bone  disease.  For  that  reason,  the  use  of  ordinary 
phosphorus  in  the  making  of  matches  has  now  been  prac- 
tically abolished,  and  a  harmless  compound  containing 
phosphorus  is  usually  substituted  in  its  place.  But  since 
friction  against  any  rough  surface  will  ignite  the  ordinary 
match,  nibbling  mice  and  busy-fingered  children  have 
often  started  disastrous  fires  with  them.  Because  of  that 
the  safety  match  was  invented,  which  will  not  ignite  by 
friction  on  any  ordinary  rough  surface. 

On  the  tip  of  the  safety  match  there  is  no  phosphorus  nor 
phosphorus  compound,  but  only  substances  that  burn 
readily  and  contain  a  great  deal  of  oxygen.  The  side  of  the 
match  box  is  used  for  a  striking  surface.  It  is  coated  with 
several  substances,  among  which  is  red  phosphorus.  The 
only  way  red  phosphorus  can  easily  be  ignited  by  friction  is 
to  rub  it  with  some  substance  that  is  rich  in  oxygen.  The 
oxygen-bearing  materials  on  the  tip  of  the  safety  match 
strike  a  spark  out  of  the  red  phosphorus,  which  in  turn 
ignites  the  match  head. 

Saving  Fuel.  —  Experiment  25.  —  (a)  After  closing  the  holes  at 
the  bottom  of  a  Bunsen  burner,  turn  on  the  gas  and  light  it.  The 
flame  is  smoky.  Heat  a  piece  of  wire  in  it.  It  heats  slowly. 


SAVING  FUEL  75 

Open  the  holes.  The  flame  ceases  to  smoke.  Place  a  wire  in  it. 
It  heats  quickly.  Regulate  the  sizes  of  the  openings  until  the 
greatest  possible  heat  is  obtained. 

(b)  By  means  of  a  ringstand  hold  a  wire  gauze  two  or  three 
inches  above  a  Bunsen  burner.  Turn  on  the  gas  and  apply  a 
lighted  match  above  the  gauze.  The  gas  above  the  gauze  will 
take  fire,  but  that  below  will  not.  (Figure  33.)  Turn  off  the  gas  and 
then  turn  it  on  again.  Now  light  the  gas  below  the  gauze.  The 
gas  above  the  gauze  does  not  ignite.  The  gauze  conducted  the  heat 
off  so  rapidly  into  the  surrounding  air  that  the  gas 
on  the  side  of  the  gauze  away  from  the  flame  was 
not  raised  to  its  kindling  temperature  and  so  did 
not  burn. 


In  Experiment  25  it  was  found  that  if  the 
holes  at  the  bottom  of  a  Bunsen  burner  are 
closed   so  that  an  abundant  supply  of  air 
(that  is,  of  oxygen  in  the  air)  is  not  mixed        FIGURE  33 
with  the   gas,  the   burner   smokes.     When 
these  holes  are  regulated  so  that  the  right  amount  of  air  is 
supplied,  there  is  a  hot  flame  and  no  smoke.     It  was  found 
in  the  second  part  of  the  experiment  that  gas  would  not 
burn  unless  it  was  raised  to  its  kindling  temperature.     This 
illustrates  what  happens,  to  a  greater  or  less  extent,  in  all 
stoves  and  furnaces  —  especially  where  soft  coal  is  burned. 

Every  one  knows  that  when  a  fresh  supply  of  soft  coal  is 
thrown  upon  a  fire,  it  smokes.  This  is  because  the  fresh 
coal  acts  as  a  blanket.  It  decreases  the  supply  of  fresh 
air  from  below,  and  lowers  the  temperature  in  the  upper 
part  of  the  stove  or  furnace.  Not  all  the  gases  from  the 
coal  that  are  driven  off  by  the  heat  below  are  burned  where 
they  are  formed,  because  the  blanket  of  coal  has  cut  down' 
the  draft  and  thus  lowered  the  supply  of  oxygen. 

These  light  gases  rise,  therefore,  into  the  upper  part  of 


76  THE    SUN'S   GIFT    OF   HEAT 

the  stove  or  furnace,  where  the  supply  of  oxygen  is  even  more 
scant  and  the  temperature  is  below  the  kindling  point  of  the 
gases.  The  result  of  this  incomplete  combustion  is  that 
part  of  the  carbon  in  the  gases  is  set  free  and  floats  away  in 
the  form  of  smoke. 

This  not  only  results  in  the  formation  of  the  smoke  nuisance 
in  cities  but  also  in  a  great  loss  of  available  heat.  It  is 
estimated  that  in  Pittsburgh  alone  the  loss  of  heat  due  to 


Courtesy  of  Underfeed  Stoker  Company  of  America 

BEFORK  INSTALLING  AN  UNDERFEED  FURNACE 

When  a  blanket  of  fresh  fuel  is  thrown  on  the  glowing  coals,  great  quan- 
tities of  carbon  and  fuel  gases  escape  as  smoke.  This  may  be  likened 
to  burning  a  candle  upside  down. 

non-combustion  of  smoke  has  been  fully  $10,000,000  in 
a  single  year.  This  is  aside  from  the  tremendous  total 
damage  to  clothing,  house  furnishings,  and  stocks  of  mer- 
chandise, and  from  its  menace  to  health. 

In  order  to  burn  the  gases  that  rise  to  the  upper  part  of 
the  stove  or  furnace,  there  must  be  a  supply  of  fresh  air 
above  the  burning  coal.  When  a  furnace  has  too  heavy  a 
draft  from  below,  and  no  supply  of  fresh  air  through  the 
feed  door,  unburned  fuel  gases  are  driven  up  the  chimney. 


ABATING  THE   SMOKE   NUISANCE  77 

With  proper  arrangements  for  putting  the  coal  upon  the 
fire  in  small  quantities  so  as  not  to  cut  off  the  draft  suddenly 
or  lower  the  temperature  of  the  upper  part  of  the  stove  too 
greatly,  a  great  saving  of  heat  can  be  realized  and  one  of 
the  worst  nuisances  of  a  modern  city  largely  avoided. 

Many  cities  require  the  use  of  smoke-consuming  furnaces 
in  all  large  buildings.  Most  of  these  are  so  arranged  that 
the  gases  formed  where  the  fresh  supply  of  coal  meets  the 


Courtesy  of  Stoker  Underfeed  Company  of  America 
AFTER  INSTALLING  AN  UNDERFEED  FURNACE 

In  this  furnace  the  fire  is  constantly  above  the  fresh  fuel,  and  the  volatile 
gases  and  carbon  are  consumed  as  they  pass  up  through  the  fire. 
This  acts  like  a  burning  candle  right  side  up. 

glowing  coals  are  conducted  "through  the  fire  and  largely 
consumed.  Contrivances  known  as  smoke  consumers  are 
sometimes  attached  to  small  furnaces.  Abating  the  smoke 
nuisance  is  a  problem  that  deserves  the  most  careful  con- 
sideration by  the  authorities  of  all  cities.  It  involves  the 
conservation  of  both  health  and  wealth. 

Control  of  Fire.  —  Fire  under  control  is  man's  best  friend. 
Fire  makes  our  homes  comfortable  in  winter,  cooks  our 
food,  lights  many  of  our  houses,  is  used  somewhere  in  the 


78 


THE    SUN'S   GIFT    OF   HEAT 


manufacturing  of  practically  everything  we  use,  fur- 
nishes power  for  most  of  our  transportation,  and  in  fact 
makes  life  livable.  But  when  fire  gets  out  of  control  it 
ruthlessly  destroys  almost  everything  it  can  touch.  The 
control  of  fire  is,  therefore,  exceedingly  important.  We 
have  seen  (page  70)  that  fire  cannot  exist  unless  oxygen  is 


FIRE  OUT  OF  CONTROL 
Fighting  the  great  conflagration  at  the  Chicago  stockyards  in  1910. 

present.  Therefore  to  control  fire  it  is  only  necessary  to 
shut  off  the  oxygen.  Closing  the  draft  of  a  stove  cuts  down 
the  supply  of  oxygen. 

When  water  is  put  on  a  fire  it  not  only  shuts  off  the  supply 
of  oxygen  but  it  also  cools  the  burning  material  below  its 
kindling  temperature.  Water,  however,  is  not  serviceable 
for  extinguishing  such  substances  as  burning  oils,  since  the 


CONTROL  OF  FIRE 


79 


burning  oil  floats  on  the  water  and  the  expansion  of  any 
generated  steam  throws  the  flaming  oil  about  and  thus 
spreads  the  fire.  In  a  case  of  this  kind,  sand  or  a  woolen 
blanket  serves  the  purpose  better. 

Wool  does  not  readily  burn,  and  when  the  blanket  is 
thrown  over  the  burning  oil,  the  air  is  shut  off  and  the 
fire  put  out.  If  one's  clothing  takes  fire  by  accident,  one 
should  never  run.  A  rug  or  a  blanket  rolled  about  the 
body  is  the  most  effective  means  of  putting 
out  the  fire.  If  one  is  outdoors,  rolling  in 
the  dust,  or  heaping  dust  on  the  flames, 
will  cut  off  the  oxygen  supply.  The  chief 
thing  to  remember  is  to  cut  off  the  air 
supply  immediately. 

Experiment  26.  —  (Teacher's  Experiment.)  — 
Get  two  or  three  bottles  of  carbon  dioxide  from 
the  chemical  laboratory,  or  prepare  it  by  pouring 
dilute  hydrochloric  acid  upon  pieces  of  limestone 
in  a  bottle  and  collecting  the  gas  over  water. 
Does  the  appearance  of  this  gas  differ  in  any 
way  from  that  of  air?  Smell  of  one  of  the 
bottles  that  has  stood  over  water  for  some  time.  FiOTRip  34.  — DIA- 

n-,i  T  ™  i.     ,  i  GRAM  OF  A   FlRE 

The  gas  has  no  odor.     Plunge  a  lighted  match       EXTINGUISHER 
into  one  of  the  bottles  containing  the  carbon 
dioxide.     What  happens?     Does  the  gas  burn  or  support  combus- 
tioh?    Slowly  overturn  a  bottle  of  the  gas  above  a  lighted  candle. 
The  candle  is  extinguished.     The  gas  falls  out  when  the  bottle 
is  overturned,  thus  showing  that  it  is  heavier  than  air.     If  the 
amount  of  carbon  dioxide  in  the  air  were  largely  increased,  what 
effect  would  it  have  upon  combustion? 

The  ordinary  chemical  fire  extinguisher  (Figure  34)  con- 
sists of  a  strong  metal  cylinder  nearly  filled  with  a  solution 
of  baking  soda.  Held  firmly  in  the  top  of  the  cylinder  is  a 


80  THE    SUN'S   GIFT    OF   HEAT 

bottle  of  sulphuric  acid.  There  is  an  opening  in  the  top  of 
the  cylinder  which  is  connected  with  the  nozzle  by  means 
of  a  short  strong  rubber  tube.  When  the  extinguisher  is 
to  be  operated,  it  must  first  be  inverted.  The  acid  falls  out 
of  the  bottle,  and  mingling  with  the  solution  of  baking  soda 
rapidly  generates  carbon  dioxide.  The  pressure  of  this 
.generating  gas  forces  the  solution  mixed  with  the  gas  out 
of  the  nozzle.  Since  carbon  dioxide  will  not  burn  and  is 
considerably  heavier  than  air,  it  helps  the  water  to  smother 
the  fire.  Chemical  fire-engines  make  use  of  this  same  gas. 

Measurement  of  Temperature.  —  It  has  been  seen  (pages 
64  and  65)  that  gases,  liquids,  and  solids  expand  when 
heated  and  contract  when  cooled.  It  has  been 
found  that  most  substances  expand  uniformly 
through  ordinary  ranges  of  temperature,  so  that 
if  this  expansion  or  contraction  is  measured,  we 
are  able  to  determine  the  change  of  temperature. 

Experiment  27.  —  Slightly  warm  the  bulb  of  an  air 
FIGURE  35  thermometer  tube  and  place  the  open  end  in  a  beaker 
half  filled  with  inky  water.  (Figure  35.)  Allow  the 
bulb  to  cool.  The  tube  will  become  partly  filled  with  the  water. 
When  the  bulb  has  become  cooled  to  the  temperature  of  its 
surroundings,  mark  the  end  of  the  water  column  with  a  rubber 
band.  Grasp  the  bulb  with  the  hand,  thus  warming  the  air  in  it. 
The  water  column  will  run  partially  out  of  the  tube  back  into  the 
beaker.  Cool  the  bulb  with  a  piece  of  ice  or  a  damp  cloth.  The 
water  will  come  farther  up  in  the  tube  than  it  did  when  simply 
exposed  to.  the  air.  We  have  here  an  apparatus  for  telling  the 
relative  temperatures  of  bodies. 

Instruments  arranged  to  show  changes  in  temperature 
by  the  amount  of  the  expansion  or  contraction  of  certain 
materials,  are  called  thermometers.  These  may  be  gas, 


MEASUREMENT   OF  TEMPERATURE  81 

liquid,  or  metal  thermometers.  There  must  be  some 
uniform  temperatures  between  which  the  expansion  shall 
be  measured  if  we  are  to  have  a  basis  of  comparison.  These 
definite  points  have  been  taken  as  the  freezing  and  boiling 
points  of  water  at  sea  level. 

Experiment  28.  —  (Teacher's  Experiment.)  —  Fill   a   four-inch 
ignition  tube  with  mercury  and  insert  a  one-hole  rubber  stopper 
having  a  straight  glass  tube  extending  through  it  and  about  20 
cm.  above  it.     (Figure  36.)     It  may  be  necessary 
to  cover  the  stopper  with  vaseline  to  keep  out          (| 
air  bubbles.     When  the  stopper  was  inserted  the 
mercury  should  have  risen  a  few  centimeters  in 
the  tube.     Mark  with  a  rubber  band  the  end  of 
the  mercury  column.     Gently  warm  the  ignition 
tube.     The   mercury   column    rises.     Cool    the 
tube  and  the  column  falls.     We  have  here  a 
crude  thermometer. 

The  substance  whose  expansion  is  most 
commonly  used  to  measure  the  degree  of 
temperature  is  mercury.  This  expands 
noticeably  for  an  increase  in  temperature  FIGURE 
and  the  amount  of  its  expansion  can  be  very 
readily  determined.  The  ordinary  thermometer  consists  of 
a  glass  tube  of  uniform  bore  which  has  a  bulb  at  one  end. 
The  bulb  and  part  of  the  tube  are  filled  with  mercury.  The 
remaining  part  of  the  tube  is  empty,  so  that  the  mercury 
can  freely  rise  or  fall.  When  the  temperature  rises,  the 
mercury  expands  and  rises,  when  the  temperature  falls,  the 
mercury  contracts  and  sinks. 

There  are  two  kinds  of  thermometer  scales  commonly 
used.  The  one  which  is  used  almost  exclusively  in  scientific 
work  and  in  those  countries  where  the  metric  system  of 
weights  and  measures  has  been  adopted,  is  called  the  Cen- 


82 


THE    SUN'S   GIFT    OF   HEAT 


U 


1 


tigrade.  In  this  scale  the  point  to  which  the  mercury 
column  sinks  when  submerged  in  melting  ice  is  marked  0°, 
and  the  point  to  which  it  rises  at  sea  level  when  immersed 
in  unconfined  steam  (the  boiling  point  of  water)  is  100°.  A 
degree  Centigrade,  then,  is  TFQ-  the  distance  the  column 
expands  when  heated  from  freezing  to  boiling. 

The  common  household  thermometer 
of  this  country  and  England  is  the 
Fahrenheit  thermometer.  It  is  named 
after  its  inventor,  who  about  two  hun- 
dred years  ago  began  the  making  of 
thermometers.  He  found  that  by  mix- 
ing ice  and  water  and  salt  he  obtained 
a  temperature  much  lower  than  that  of 
freezing  water.  This  temperature  he 
took  as  his  zero  point.  In  this  scale  the 
point  at  which  ice  and  snow  melt  is 
marked  32°,  and  the  point  at  which 
water  boils  at  sea  level  is  marked  212°. 
The  distance  between  the  boiling  point 
and  freezing  points  is  divided  into  180 
equal  parts,  or  degrees.  A  degree 
Fahrenheit,  then,  is  -^  the  distance  the 
column  expands  when  heated  from  freez- 
ing to  boiling,  instead  of  yinr  as  in  the 
Centigrade  scale.  (Figure  37.) 

There  are  a  number  of  different  designs  of  thermometers. 
Some  are  for  measuring  very  high,  others  for  measuring  very 
low,  temperatures.  Thermometers  are  also  constructed  so 
as  to  be  self-recording.  (Figure  38.) 

The  Measurement  of  Heat.  —  Experiment  29.  —  In  each  of 
two  beakers  or  tin  cups  weigh  out  100  g.  of  water.  Carefully  heat 


FIGURE  37. — CENTI- 
GRADE AND  FAH- 
RENHEIT SCALES 
COMPARED 


THE  MEASUREMENT   OF   HEAT 


83 


one  of  the  beakers  until  the  water  when  thoroughly  stirred  shows 
a  temperature  of  90°  C.  Cool  the  other  beaker  till  the  tempera- 
ture of  the  water  is  10°  C.  Pour  the  water  from  one  beaker  into 
the  other,  and  after  thoroughly  stirring  note  the  resulting  tempera- 
ture. Use  a  chemical  thermometer  to  determine  the  temperatures. 
Weigh  out  100  g.  of  fine  No.  10  shot  in  a  tin  cup  and  100  g.  of 
water  in  another.  Place  the  cup  containing  the  shot  in  boiling 
water  and  allow  it  to  re- 
main, stirring  the  shot  occa- 
sionally, until  its  tempera- 
ture is  90°  C.  Cool  the 
water  in  the  other  beaker 
until  its  temperature  is 
10°  C.  Determine  the  tem- 
peratures exactly  and  then 
pour  the  shot  into  the 
water.  After  thoroughly 
stirring  determine  the  tem- 
perature of  the  mixture. 
Which  has  the  highest 

temperature,  the  mixture  of  water  and  water  or  the  mixture  of  shot 
and  water? 

Since  heat  plays  such  an  important  part  in  the  activities 
of  the  eartn,  we  need  to  know  how  to  measure  it.  There 
is  a  great  difference  between  temperature  and  the  amount 
of  heat.  The  amount  of  heat  in  a  spoonful  of  water  at 
100°  would  be  very  much  less  than  in  a  pailful  of  water 
at  10°.  It  would  require  more  heat  to  raise  a  pond  of 
water  a  small  part  of  a  degree  than  to  raise  a  kettleful 
many  degrees.  That  is  why  large  bodies  of  water,  although 
their  temperatures  never  greatly  change,  are  able  to  absorb 
and  to  give  out  great  amounts  of  heat. 

Not  only  does  the  amount  of  heat  necessary  to  raise  the 
temperature  of  different  quantities  of  the  same  substance 
vary,  but  the  amount  of  heat  necessary  to  raise  the  tem- 


FIGURE  38. — A  SELF-RECORDING 
THERMOMETER 


84  THE    SUN'S   GIFT    OF    HEAT 

perature  of  equal  quantities  of  different  substances  also 
varies.  If  a  pound  of  water  and  a  pound  of  olive  oil  are 
placed  side  by  side  in  similar  dishes  on  a  stove,  it  will  be 
found  that  the  olive  oil  increases  in  temperature  about 
twice  as  fast  as  the  water,  i.e.  it  takes  about  twice  as  much 
heat  to  raise  water  as  it  does  to  raise  the  same  weight  of 
olive  oil  one  degree.  In  fact,  it  takes  more  heat  to  raise 
a  given  weight  of  water  one  degree  than  it  does  to  raise 
the  same  weight  of  almost  any  other  known  substance. 

In  Experiment  29,  the  resulting  temperature  from  the 
water  mixture  was  much  higher  than  from  the  water  and 
shot  mixture.  The  shot  has  much  less  capacity  for  heat. 
The  quantity  of  heat  required  to  raise  the  temperature  of  a 
certain  mass  of  a  substance  one  degree  compared  to  the 
quantity  of  heat  required  to  raise  the  same  mass  of  water 
one  degree  is  called  the  specific  heat  of  that  substance. 
The  specific  heat  of  olive  oil  is  .47,  of  shot  .03.  That  is, 
it  takes  .47  as  much  heat  to  raise  a  given  mass  of  olive  oil 
and  .03  as  much  heat  to  raise  a  given  mass  of  shot  one 
degree  as  it  does  to  raise  a  corresponding  mass  of  water 
one  degree.  In  order  to  compare  different  quantities  of  heat, 
physicists  have  taken  as  the  unit  of  measure  the  quantity 
of  heat  required  to  raise  the  temperature  of  one  gram  of 
water  through  one  degree  C.  This  unit  is  called  a  calorie. 

The  Effect  of  Heat  upon  the  Condition  of  a  Substance.  — 

Experiment  30.  —  Having  filled  two  tin  cups  or  beakers  of  the  same 
size  to  an  equal  height,  one  with  water  and  the  other  with  a  mix- 
ture of  water  and  ice,  place  them  side  by  side  on  a  stove  or  over 
Bunsen  burners  so  adjusted  as  to  give  approximately  the  same 
amount  of  heat.  (Figure  39.)  Stir  each  with  a  chemical  thermom- 
eter, and  make  a  note  of  its  temperature. 

After  heating  a  few  minutes,  stir  again  and  note  the  tempera- 
ture. Have  there  been  like  changes  in  the  temperatures  of  the 


LATENT  HEAT 


85 


two  cups?  Continue  to  stir  and  note  the  changes  until  the  ice  is 
melted.  Do  your  notes  show  that  like  amounts  of  heat  have  pro- 
duced like  changes  of  temperature  in  the  two  cups?  Continue  to 
heat,  stirring  and  noting  the  temperatures  occasionally.  Is  there 
now  an  approximately  equal  rise  of  the  temperatures  of  the  water 
in  the  cups? 

When  the  water  in  one  cup  begins  to  boil,  does  its  temperature 
continue  to  rise  as  fast  as  that  of  the  water  in  the  other  cup?  What 
apparently  became  of  the 
heat  delivered  to  the  ice- 
water  before  the  ice  melted? 
What  apparently  became 
of  the  heat  delivered  to 
the  water  while  it  is  boil- 
ing? 

The  preceding  experi- 
ment shows  that  heat  is 
absorbed  in  melting  ice, 
an'd  that  the  heat  so 
absorbed  does  not  raise 
the  temperature  of  the 

ice.  It  also  shows  that  heat  changes  water  into  steam,  and 
that  although  very  much  heat  was  applied  none  of  it  was 
used  in  raising  the  temperature  of  the  boiling  water  but  all 
of  it  in  changing  the  condition  of  the  water. 

Carefully  performed  experiments  show  that  it  takes  80 
times  as  much  heat  to  change  a  gram  of  ice  at  0°  C.  into 
water  at  0°  C. ;  and  about  536  times  as  much  to  change 
a  gram  of  water  at  100°  C.  into  steam  at  100°  C.  as  it  does  to 
raise  the  temperature  of  the  same  mass  of  water  one  degree 
C.  The  heat  absorbed  in  changes  of  this  kind  is  called 
latent  heat.  It  is  all  given  out  again  when  the  water  freezes 
or  the  steam  condenses. 

This  explains  why  ice  melting  in  a  refrigerator  takes  so 


FIGURE  39 


86 


THE    SUN'S   GIFT    OF   HEAT 


much  heat  from  the  air  and  food  about  it  and  keeps  them 
cool.  It  also  explains  why  so  much  heat  is  given  out  when 
the  steam  in  a  steam  radiator  condenses  into  water,  and 
why  steam  heating  is  the  most  effective  way  of  heating 
houses  in  cold  climates. 

Many  of  us  have  noticed  that  when  we  have  a  quiet 
snowfall  the  temperature  usually  rises.  This  is  because  the 
heat  given  out  by  the  changing  of  the  vapor  in  the  air  into 
snow  is  not  carried  by  the  air  currents 
to  another  region  but  warms  the  local 
atmosphere.  Many  similar  phenomena 
are  explained  by  this  experiment. 


FIGURE  40.  —  COMPAR- 
ATIVE EFFECTS  OF 
HEAT 


The  Transference  of  Heat.  —  Some 
one  has  stated  a  truth  playfully  in 
saying  that  "  no  substance  is  ever 

The  amount  of  heat  re-      selfish     with     the     heat     it     pOSSCSSCS." 

quired  to  change  the    Any  hot  object  left  for  a  long  enough 

smaller  mass  of  water        .  . 

into  steam  without    time  in  cooler  surroundings  will  yield 

altering  its  tempera-      up  ^  ^  m^   {t  .g  Qf  ^  ^^  tem_ 


ture  would  raise  the 

temperature  of  the    perature  as  its  surroundings.     Any  cold 

larger    volume     one        ,  .  ,         ,      .  . . 

degree.  object  placed  in  warm  surroundings 

will  receive  heat  until  it  is  eventually 
of  the  same  temperature  as  its  surroundings. 

If  water  is  placed  on  a  hot  stove  it  will  absorb  heat  until 
it  passes  away  in  steam.  If  hot  water  is  allowed  to  stand 
in  a  room,  it  will  give  off  its  heat  until  its  temperature  falls 
to  that  of  the  room.  When  ice  is  placed  in  a  refrigerator 
the  heat  of  the  contents  of  the  refrigerator  is  yielded  up  to 
the  ice  and  melts  it.  If  a  refrigerator  could  be  so  con- 
structed that  no  warmth  could  reach  its  interior,  the  contents 
would  eventually  become  as  cold  as  the  ice. 


THE   TRANSFERENCE   OF  HEAT  87 

Experiment  31.  —  Cut  off  15  cm.  of  No.  10  copper  and  No.  10 
iron  wire  and  the  same  length  of  glass  rod  of  about  the  same  di- 
ameter. Holding  each  of  these  by  one  end  place  the  opposite  end 
in  the  flame  of  a  Bunsen  burner.  Which  of  the  three  conducts  the 
heat  to  the  hand  first  ? 

Experiment  32.  —  Fill  a  test  tube  about  f  full  of  cold  water.  Hold- 
ing the  tube  by  the  bottom  carefully  heat  the  top  part  of  the  water 
until  it  boils.  Be  sure  that  the  flame  does  not  strike 
the  tube  above  the  water,  else  the  tube  will  break. 
(Figure  41.)  A  little  piece  of  ice  in  the  bottom  of 
the  test  tube  makes  the  action  more  apparent.  A 
bit  of  wire  gauze  or  a  wire  stuffed  into  the  test  tube 
will  prevent  the  ice  from  coming  to  the  surface. 
Water  conducts  heat  poorly.  The  hot  water  does 
not  sink.  Do  you  conclude  that  the  warm  water  is  heavier  or 
lighter  than  the  colder  water  ? 

Through  solid  substances,  such  as  metals,  heat  travels 
quite  readily ;  through  others,  such  as  glass,  less  rapidly. 
In  Experiment  31,  we  found  that  heat  traveled  along  some 
rods  faster  than  it  did  along  others.  In  no  case,  however, 
was  there  any  indication  that  there  was  a  transference  of  the 
particles  composing  the  rods.  In  the  boiling  of  the  water 
at  the  top  of  the  test  tube,  there  was  no  indication  that 
the  water  particles  moved  to  the  bottom  of  the  tube.  In 
these  cases,  the  heat  is  simply  transferred  from  molecule 
to  molecule. 

This  kind  of  heat  transference  is  called  conduction.  In 
transference  by  conduction  each  molecule  acts  as  a  mes- 
senger, passing  the  heat  energy  on  to  another  that  it  touches. 
If  two  different  substances  touch  each  other,  the  molecules 
of  one  substance  may  conduct  heat  to  the  molecules  of  the 
other ;  but  the  two  substances  must  be  touching  each  other 
or  the  method  of  transference  cannot  be  called  conduction. 

Conductors  may  be  good  or  bad,  as  was  shown  by  the 


88  THE    SUN'S   GIFT   OF   HEAT 

different  materials  used  in  the  experiments.  One  of  the 
reasons  why  we  use  iron  for  our  radiators  is  that  the  heat 
of  the  steam  may  readily  pass  from  the  inside  to  the  out- 
side of  the  radiator.  We  cover  our  steam  pipes  with  as- 
bestos when  we  wish  to  retain  the  heat,  because  asbestos 
is  a  poor  conductor  and  will  keep  the  heat  in  the  pipes. 

On  a  cold  day  good  conductors  of  heat  feel  colder  than 
other  objects  because  they  quickly  conduct  the  heat  away 
from  the  hand.  For  that  reason,  a  metal  door  knob  seems 
much  colder  than  the  door  in  winter.  On  a  very  warm  day 
good  conductors  feel  hotter  than  other  objects  because  they 
conduct  their  heat  to  the  hand  rapidly.  The  metal  knob, 
therefore,  seems  much  warmer  than  the  door  when  the  bright 
sun  is  shining  on  them  both  in  summer. 

This  explains  why  tile  and  concrete  floors  feel  cold,  and 
why  we  cover  them  with  rugs,  which  are  poor  conductors 
of  heat.  A  woolen  blanket  feels  warm,  and  a  cotton  sheet 
cold,  for  the  same  reason.  There  is  really  no  difference 
between  the  warmth  of  these  objects  if  they 
are  in  surroundings  of  the  same  temperature. 

Experiment  33.  —  Hold  a  piece  of  burning  paper 
under  a  bell  jar  held  mouth  downward.  (Figure 
42.)  Notice  the  air  currents  as  indicated  by  the 
smoke.  Paper  soaked  in  a  moderately  strong 
solution  of  saltpeter  and  dried  burns  with  a  very 
FIGURE  42  smoky  flame. 

Experiment  34.  —  Fill  a  500  cc.  round-bottomed 
flask  half  full  of  water  and  place  on  a  ringstand  above  a  Bunsen 
burner.  (Figure  43.)  Stir  in  a  little  sawdust.  Some  of  it  should 
fall  to  the  bottom  of  the  flask.  Gently  heat  the  bottom  of  the 
flask.  Notice  the  currents. 

When  the  burning  paper  was  held  under  the  bell  glass,  and 
when  the  water  was  heated  at  the  bottom  of  the  flask,  cur- 


THE   TRANSFERENCE   OF  HEAT 


FIGURE  43 


rents  were  seen  to  be  developed.  The  heated  and  expanded 
air  and  water  rose.  Here  again  the  heat  was  transferred 
by  conduction,  but  it  was  helped  by  the 
upward  movement  of  the  heated  water 
and  air.  These  upward  movements  of 
the  water  and  the  air  are  known  as  con- 
vection currents.  The  efficiency  of  the  hot 
water  and  hot  air  furnaces  which  heat  our 

houses  is 
due  to  the 
convection 
currents. 
We  shall 
find  later 

that  if  it  were  not  for  cdn- 
vection  currents  there  would 
be  no  winds  nor  ocean  cur- 
rents. 

Whether  we  heat  a  test 
tube  of  water  from  above  or 
from  below,  the  heat  is  car- 
ried by  conduction  from  one 
molecule  to  another.  But 
FIGURE  "FU^CE"  WATER  when  we  heat  *  from  bel°w, 

As  the  water  in  the  boiler  begins  to  the    P^CSS    is    hastened    by 

heat,  convection   currents  are  set  convection  Currents, 
up.     Cold  water,  which  is  heavier, 
flows  from  the  radiators  down  into         It     an    incandescent    lamp 


fire  is  maintained  in  the  furnace,  the    hand    held    a    little    dis- 
there  is  constant  circulation.    Since  »  ,  ,  u    lu 

water  expands  under  heat,  an  over-  tance    from    the    glass     bulb, 

flow  tank  must  be  provided   to  the   hand    will    be  warmed, 

prevent  explosion  of  the  pipes  or 

boiler.  although  the  glass  bulb  itself 


90 


THE   SUN'S   GIFT    OF   HEAT 


(a  poor  conductor  of  heat)  remains  cool  for  a  time.  When 
the  lamp  was  made,  air  was  taken  from  the  bulb,  and  so 
the  white-hot  filament  is  surrounded  by  almost  empty  space 
(vacuum).  The  heat,  therefore,  cannot  travel  to  the  hand 
by  convection  currents,  because  there  is  no  air  nor  other 
substance  in  contact  with  the  filament.  The  hand  is  not 
warmed  by  convection  currents  from  the  glass,  because  the 
bulb  is  still  cool.  The  sensation  of  heat  can- 
not be  due  to  conduction,  because  the  air  which 
surrounds  the  bulb  is  not  in  contact  with  the 
hot  filament.  Besides,  air  is  an  even  poorer 
conductor  of  heat  than  glass,  and  the  glass 
itself  does  not  become  hot  for  some  little  time. 
There  must,  therefore,  be  another  mode  of 
transferring  heat  besides  conduction  and  con- 
vection. It  also  appears  that  in  this  method 
of  transferring  no  material  substance  is  neces- 
sary. This  is  shown  by  the  fact  that  the  hot 
filament  is  surrounded  by  an  almost  perfect 
vacuum.  Astronomers  tell  us  that  there  is 
no  material  medium  between  our  atmosphere 
and  the  sun. 

The  heat  of  the  sun  travels  to  us  with  the  tremendous 
speed  of  light,  186,000  miles  a  second,  but  does  not  warm 
the  intervening  space  because  there  is  no  matter  in  it  to 
be  warmed.  Radiation  is  the  name  given  to  this  method  of 
heat  transference.  If  heat  did  not  travel  in  this  way,  the 
earth  would  be  uninhabitable.  The  conduction  process  is 
very  slow  when  compared  with  radiation. 


FIGURE  45 


Conserving   Heat.  —  Heat    is    so    essential    to    life    and 
happiness  that  it  is  often  necessary  to  provide  means  for 


CONSERVING  HEAT 


91 


preventing  its  escape.  We  build  thick  walls  to  our  houses 
in  order  that  the  heat  from  our  stoves  and  furnaces  may  not 
escape.  We  put  on  clothing  in  order  that  the  heat  of  the 
body  may  be  retained.  Ovens  of  cookstoves  are  surrounded 
by  air  spaces  and  non-conducting  materials  so  that  the  heat 
will  not  be  lost.  In  fact  there  are  scores  of  arrangements 
in  every  home  for  conserving  heat. 

Dark  surfaces  absorb  heat  more  readily  than  light  surfaces, 
and  thus  increase  more  rapidly  in  temperature.  Light 
surfaces  reflect  heat,  and  absorb 
it  very  slowly.  This  is  why  we 
wear  dark  clothing  in  winter 
and  light-colored  clothing  in 
summer.  Dark  surfaces  not 
only  absorb  heat  more  readily 
but  they  radiate  it  more  rapidly. 
Light  surfaces  are  slow  to  heat 
up,  and  when  they  are  heated 
up  they  are  just  as  slow  to 
radiate  their  heat.  There  is 
the  same  difference  in  these 
respects  between  smooth  surfaces  and  rough  surfaces  as 
between  light  and  dark  surfaces, 

The  fireless  cooker  (Figure  46)  is  a  device  to  save  heat  in 
cooking.  It  consists  of  two  boxes,  one  within  the  other  and 
separated  from  each  other  on  all  sides  by  a  space  of  several 
inches.  This  space  is  filled  with  sawdust,  ground  cork,  as- 
bestos, or  any  other  substance  that  is  a  poor  conductor  of 
heat.  A  tightly  fitting  cover  is  provided,  containing  similar 
non-conducting  material.  The  food  to  be  cooked  is  heated 
on  the  stove  in  a  covered  vessel,  and  this  is  placed  within 
the  cooker.  Since  the  heat  can  escape  only  very  slowly,  the 


REVOLVING  DOORS 
An  arrangement  to  conserve  heat. 


92 


THE    SUN'S   GIFT    OF   HEAT 


FIGURE  46.  —  DIAGRAM  OF  A 
FIRELESS  COOKER 


food  remains  at  nearly  the  boiling  point  for  hours,  and  is 
thus  cooked.  In  most  cookers,  heated  pieces  of  soap- 
stone  are  placed  above  and 
below  the  dish  containing  the 
food.  Soapstone  has  a  large 
capacity  for  heat.  (Page  84.) 
The  fireless  cooker  can  also 
be  used  as  a  refrigerator  if 
the  food  is  cooled  before  being 
placed  in  it  or  if  ice  is  placed 
in  it  with  the  food.  When 
the  cooker  is  used  as  a  refrigerator,  the  insulated  walls  are 
very  slow  to  conduct  the  heat  of  the  atmosphere  to  the 
cold  food,  just  as  they  were  slow  to  con- 
duct the  inside  heat  to  the  cooler  sur- 
rounding atmosphere.  The  non-conducting 
character  of  the  walls  protects  either  way. 
For  that  reason  the  walls  of  a  fireless 
cooker  are  similar  to  those  of  a  refrigerator. 
Snow  on  the  ground  in  winter  prevents 
the  heat  from  leaving  the  ground  and  the 
ground  from  being  deeply  frozen,  just  as 
the  sawdust  and  other  materials  in  the 
walls  of  the  cooker  prevent  the  heat  from 
being  conducted  rapidly  away  from  the 
cooker.  That  is  one  reason  why  farmers 
like  a  snowy  winter. 

The  thermos  bottle  (Figure  47)  is  similar 
to    the    fireless   cooker    in   principle.      It 
consists  of  two  glass  bottles,  one  placed 
inside  the  other,  sealed  together  at  the  neck.     Before  the 
bottles  are  sealed   together  the  air  between   them    is   re- 


FIGCJRE  47.  —  DIA- 
GRAM OF  A  THER- 
MOS BOTTLE 


SUMMARY  93 

moved.  Heat,  therefore,  cannot  pass  from  the  inner  bottle 
by  conduction  or  convection.  To  retard  the  passage  of 
radiant  heat,  the  inner  walls  of  the  vacuum  space  are  finished 
with  bright  reflecting  surfaces. 

Note  to  Students.  —  Both  the  Centigrade  and  the  Fahrenheit 
scale  are  used  in  later  discussions  in  this  book.  The  student  has 
been  accustomed  to  the  English  or  Fahrenheit  scale  in  everyday 
life,  and  so  occasionally 'the  use  of  this  scale  prevents  unnecessary 
confusion.  On  the  other  hand,  the  Centigrade  scale  is  preferred  in 
scientific  work,  and,  like  all  the  metric  scales,  is  the  rational  system. 
It  is,  therefore,  used  frequently  hereafter  hi  order  to  familiarize 
students  with  it.  In  occasional  discussions  where  one  scale  is  used, 
approximate  equivalents  in  the  other  scale  are  added  in  parentheses. 

The  following  rules  will  be  found  useful  in  changing  readings 
from  one  scale  to  the  other : 

To  change  Fahrenheit  to  Centigrade,  subtract  32  from  the  number 
of  degrees  and  multiply  the  remainder  by  f . 

70°  F.  =  (70  -  32)  X*  =  2H°C. 

To  change  Centigrade  to  Fahrenheit,  divide  the  number  of  degrees 
by  \  and  add  32. 

_  10°  C.  =  (-  10  -=-  $•)  +  32  =  14°  F. 

SUMMARY 

The  sun  is  the  source  of  the  heat  and  light  of  the  earth. 
Heat  has  the  capacity  to  do  work,  and  is  therefore  a  form  of 
energy.  The  sun  is  the  source  of  the  energy  on  the  earth. 
If  a  body  has  the  ability  to  do  work  without  actually  being 
at  wrork,  it  is  said  to  have  potential  energy ;  the  energy  of  a 
body  at  work  is  called  kinetic.  There  are  different  forms 
of  energy,  such  as  heat,  light,  electricity,  gravitation,  chemi- 
cal energy,  and  mechanical  energy.  Energy  can  neither  be 
created  nor  destroyed,  but  one  form  of  energy  may  readily 
be  changed  into  another.  Heat  causes  most  substances  to 


94  THE   SUN'S  GIFT   OF  HEAT 

expand;  withdrawal  of  heat  causes  most  substances  to 
contract. 

Mass  is  the  amount  of  matter  in  a  body.  Volume  is  the 
amount  of  space  a  body  occupies.  Density  depends  on  the 
amount  of  matter  in  a  given  volume.  Weight  is  the  measure 
of  the  earth's  attraction,  or  gravity,  for  any  mass. 

Heat  is  molecular  energy.  Sufficient  heat  will  change 
solids  to  liquids  and  liquids  to  gases'.  The  most  common 
way  of  producing  heat  is  by  burning.  Burning  is  a  chemical 
process  in  which  atoms  of  oxygen  unite  with  atoms  of  fuel 
elements,  such  as  carbon  and  hydrogen.  Heat  may  also 
be  produced  by  chemical,  mechanical,  or  electrical  action. 
The  temperature  to  which  a  substance  must  be  brought  be- 
fore it  will  burn  is  called  its  kindling  temperature.  Keep- 
ing fuel  elements  in  a  furnace  at  their  kindling  temperature 
and  providing  just  the  right  oxygen  supply  are  the  two 
problems  to  be  solved  in  saving  fuel  and  abating  the  smoke 
nuisance.  Fire  can  always  be  extinguished  if  the  supply  of 
air  that  reaches  it  can  be  shut  off. 

In  gas,  metal,  and  liquid  thermometers,  substances  that 
expand  and  contract  uniformily  through  ordinary  tempera- 
tures are  employed.  The  two  most  commonly  used  ther- 
mometer scales  are  the  Centigrade  and  the  Fahrenheit .  Some 
substances  require  more  heat  than  others  to  raise  their 
temperatures.  Water  absorbs  more  heat  than  almost  any 
other  known  substance.  When  a  solid  changes  to  a  liquid 
or  a  liquid  to  a  gas,  a  tremendous  amount  of  heat  is  ab- 
sorbed which  does  not  raise  the  temperature.  When  the 
changes  are  reversed,  this  heat  is  given  out. 

Heat  may  be  transferred  by  conduction,  convection  cur- 
rents, and  radiation.  The  principle  of  heat  transference 
accounts  for  the  efficiency  of  stoves  and  furnaces,  as  well  as 


QUESTIONS  95 

of  refrigerators.  Fireless  cookers,  thermos  bottles,  revolving 
doors,  refrigerators,  etc.,  are  devices  to  prevent  rapid  trans- 
ference of  heat. 

QUESTIONS 

When  we  say  a  body  possesses  energy,  what  do  we  mean?  Give 
an  example  of  each  of  the  two  kinds  of  energy. 

You  have  used  a  great  deal  of  energy  to-day.  Where  did  this 
energy  come  from? 

What  is  the  Law  of  the  Conservation  of  Energy?  What  do  we 
mean  when  we  speak  of  "lost  energy"? 

Where  have  you  seen  the  effects  of  expansion  due  to  heat? 

Explain  the  difference  between  mass,  volume,  density,  and 
weight. 

What  is  meant  by  saying  that  a  substance  is  hot? 

Why  are  iron  and  type-metal  better  suited  for  casting  than 
copper  and  zinc? 

Describe  three  ways  of  producing  heat. 

How  are  fires  started? 

What  are  the  conditions  necessary  for  obtaining  all  the  heat 
possible  from  fuel? 

Describe  the  different  means  you  would  employ  in  putting  out 
fire. 

France  uses  the  Centigrade  thermometer  scale.  If  the  tempera- 
ture of  Paris  is  reported  as  25°  C.,  what  would  the  corresponding 
temperature  be  in  the  thermometer  scale  generally  used  in  the 
United  States? 

Ponds  near  the  Great  Lakes  freeze  entirely  over.  Why  do  not 
the  Great  Lakes  freeze?  \ 

Why  would  it  not  be  as  well  to  put  ten  pounds  of  ice-cold  water 
into  the  refrigerator  as  ten  pounds  of  ice? 

In  what  ways  is  heat  transferred? 

Describe  how  you  would  prepare  from  the  ordinary  materials 
you  have  at  hand  a  crude,  inexpensive,  fireless  cooker. 


CHAPTER  V 

THE  ATMOSPHEKE  AND  ITS   SEEVIOE  TO  MAN 

The  Origin  of  the  Atmosphere.  —  When  the  earth  cooled 
from  its  original  intensely  hot  condition,  the   substances 


BLUE  HILL  OBSERVATORY,  MILTON,  MASSACHUSETTS 

One  of  the  first  places  in  America  where  conditions  of  the  upper 

atmosphere  were  studied. 

which  did  not  chemically  combine  to  form  liquids  and  solids, 
or  which  required  a  very  low  temperature  for  their  consoli- 
dation, were  left  still  in  the  gaseous  state  around  the  solid 
96 


THE   COMPOSITION   OF   THE   AIR  97 

core.  This  gaseous  envelope,  composed  of  these  substances 
surrounding  the  earth,  we  call  the  atmosphere.  Some  of  these 
gases  are  inert;  that  is,  they  do  not  readily  form  chemical 
combinations  with  other  substances.  Others  have  formed 
extensive  combinations,  but  they  exist  in  such  large  quanti- 
ties that  they  were  not  thereby  exhausted. 

The  Composition  of  the  Air.  —  Experiment  35.  —  (Teacher's' 
Experiment.)  —  Having  rounded  out  a  cavity  in  a  small  flat  cork, 
cover  the  cavity  and  surface  around  it  with  a  thin  layer  of  plaster 
of  Paris.  After  the  plaster  has  set  and  become  thoroughly  dry, 
float  the  cork  on  a  dish  of  water  with  the  cavity  side  up.  Place 
a  piece  of  phosphorus  as  large  as  a  pea  in  the 
cavity  and  carefully  light  it.  (Figure  48.)  (Great 
care  must  be  taken  in  handling  phosphorus,  as  it 
ignites  at  a  low  temperature  and  burns  with 
great  fierceness.  It  must  always  be  cut  and 
handled  under  water.) 

As  soon  as  the  phosphorus  is  lighted,  cover 
it  with  a  wide-mouthed  bottle.     Be  sure  that          FIGURE  48 
the  mouth  of  the  bottle  is  kept  slightly  under 
water.     The  water  will  be  found  to  rise  in  the  bottle.     The  phos- 
phorus soon  ceases  to  burn.     White  fumes  are  formed,  but  these 
soon  clear  up.    A  clear  gas  is  left  in  the  bottle,  but  this  cannot 
be  air;   for  if  it  were,  the  phosphorus  would  have  continued  to 
burn  in  it,  since  it  burns  in  air.     If  it  were  not  for  this  property 
of  not  permitting  phosphorus  to  burn,  the  gas  left  in  the  bottle 
could  not  be  distinguished  by  ordinary  means  from  air. 

The  gas  fills  more  than  three  fourths  of  the  bottle,  so  that  more 
than  three  fourths  of  the  air  is  composed  of  a  gas  which  does  not 
support  combustion.  This  gas  is  called  nitrogen.  The  other  constitu- 
ents of  the  air  must  also  be  transparent  colorless  gases,  since  the  air 
is  transparent  and  colorless.  The  most  important  of  these  is  called 
oxygen.  The  phosphorus  united  with  this  and  formed  the  white 
fumes.  These  fumes  dissolved  in  the  water,  leaving  the  nitrogen. 

Be  careful  to  put  the  cork  on  which  the  phosphorus  was  burned 
in  a  place  where  it  cannot  cause  a  fire. 


98       THE   ATMOSPHERE   AND    ITS   SERVICE    TO   MAN 

Although  the  air  appears  to  be  a  simple  gas  and  was  so 
considered  until  the  end  of  the  eighteenth  century,  it  has 
been  shown  to  be  a  mixture  of  several  different  colorless  gases. 
One  of  these,  oxygen,  supports  combustion,  as  we  have 
already  learned;  another,  nitrogen,  neither  burns  nor  sup- 
ports combustion.  These  two  gases  make  up  by  far  the 
greater  part  of  the  air  about  us,  and  occur  in  the  proportion 
of  about  one  part  of  oxygen  to  four  parts  of  nitrogen.  Car- 
bon dioxide  is  also  found  in  the  air  in  the  proportion  of  about 
3  parts  to  10,000.  There  are  in  addition  very  small  quan- 
tities of  several  other  gases,  but  these  are  not  of  suffi- 
cient importance  to  be  studied  here.  Besides  the  gases, 
the  air  contains  other  matter,  such  as  water  vapor,  dust 
particles,  and  microbes. 

Almost  all  of  us  have  had  occasion  to  observe  that  if  there 
is  a  slight  leak  of  gas  from  the  gas  stove  in  the  kitchen,  the 
"  smell  of  gas  "  will  permeate  the  whole  house.  It  makes 
no  difference  whether  there  are  currents  of  air  to  carry  the 
gas  or  not.  Gases,  whether  heavy  or  light,  mix  readily 
with  each  other,  or  diffuse.  As  a  rule,  therefore,  the  propor- 
tion of  oxygen,  nitrogen,  carbon  dioxide,  and  other  gases 
is  the  same  for  all  places  on  the  surface  of  the  earth. 

Oxygen  is  the  most  important  part  of  the  air  to  animals, 
for  without  it  they  could  not  live.  They  breathe  in  oxygen, 
and  breathe  out  carbon  dioxide.  All  the  heat  and  energy 
animals  have  is  due  to  their  power  of  combining  oxygen  writh 
carbon.  Plants  also  have  need  of  oxygen,  but  to  a  smaller 
degree  than  animals. 

The  nitrogen  is  needed  to  dilute  the  oxygen.  If  oxygen 
were  undiluted,  animals  could  not  live;  and  a  fire  once 
started  would  burn  up  iron  as  readily  as  it  now  does  wood. 
Plants  and  animals  need  nitrogen  too,  but  it  is  of  no  use  to 


THE  COMPOSITION  OF  THE  AIR  99 

them  as  it  occurs  free  in  the  air.  Certain  very  low  and 
minute  forms  of  life  known  as  bacteria  have  the  power  to 
take  nitrogen  from  the  air  and  to  prepare  it  for  the  use  of 
plants.  The  nitrogen  must  be  chemically  compounded  with 
other  substances  before  it  can  be  used  either  by  animals  or 
plants  as  food. 

Plants  need  carbon  dioxide  as  much  as  animals  need 
oxygen.  The  growth  of  a  plant  is  due  to  the  power  it  has 
of  tearing  apart  the  carbon  dioxide  by  the  help  of  the  sun 
and  of  building  the  carbon  into  its  structure.  It  returns 
the  oxygen  to  the  air  to  be  used  again  by  the  animals  and 
the  plants.  By  far  the  greater  part  of  plants  is  made  from 
the  carbon  which  they  get  from  carbon  dioxide. 

Animals  have  not  the  bodily  power  of  breaking  down 
carbon  dioxide  to  obtain  oxygen  from  it ;  consequently  they 
smother  in  this  gas.  Since  men  and  other  animals  are  con- 
stantly using  up  the  oxygen  in  the  surrounding  atmosphere 
and  are  breathing  out  carbon  dioxide,  the  rooms  where  they 
stay  must  be  properly  ventilated. 

Carbon  dioxide  is  heavier  than  air  and  has  a  tendency  to 
accumulate  in  wells  and  unventilated  mines.  Workmen 
caught  in  this  gas  are  smothered  exactly  as  if  by  drowning. 
Frequently  in  coal-mine  explosions  so  much  carbon  dioxide 
is  formed  that  but  little  free  oxygen  remains ;  and  so  miners 
often  escape  an  explosion  only  to  be  smothered  by  the  carbon 
dioxide  (choke  damp,  as  they  call  it).  Before  going  down 
into  a  well  or  cistern,  careful  workmen  always  lower  a  lighted 
candle  to  test  for  the  presence  of  carbon  dioxide.  If  this  is 
present  in  large  quantities  the  candle  is  extinguished. 

In  some  places,  such  as  Dog  Grotto  near  Naples,  Italy, 
and  Death  Gulch  in  Yellowstone  Park,  carbon  dioxide  is 
being  steadily  emitted  from  the  ground.  Since  these  places 


100     THE   ATMOSPHERE   AND    ITS   SERVICE    TO   MAN 

are  low  and  sheltered  from  the  wind,  the  heavy  gas  accumu- 
lates in  sufficient  quantities  to  be  fatal  to  animals  that  at- 
tempt to  pass  through  them. 

Moisture  in  the  Air :  Evaporation.  —  The  atmosphere 
at  all  times  and  under  all  conditions  contains  some  mois- 
ture. In  the  air  of  even  the  driest  desert  there  is  some 
water  vapor.  Plants  and  animals  both  need  it.  Were 
it  not  for  the  moisture  in  the  air  there  would  be  no  rain ; 
and  without  rain  no  land  life  could  exist.  Thus  the  air, 
which  contains  oxygen  and  water  vapor  for  both  plants 
and  animals,  carbon  dioxide  for  plants,  and  nitrogen  to 
dilute  the  oxygen,  is  one  of  the  most  important  life  factors 
of  the  earth. 

Experiment  36.  —  Carefully  weigh  a  dish  of  water  and  put  it  in 
a  convenient  place  where  there  is  free  access  of  air.  After  some 
hours  weigh  it  again.  What  causes  the  change  of  weight  ?  Try 
this  experiment  with  a  test  tube,  a  watch  crystal,  and  a  wide- 
mouthed  beaker,  under  various  conditions  and  in  various  places. 

When  water  is  exposed  to  the  air,  it  gradually  disappears 
into  the  surrounding  atmosphere.  This  process  is  called 
evaporation.  Evaporation  takes  place  only  from  the  sur- 
face of  a  body  of  water.  It  may  occur  at  any  temperature ; 
but  since  heat  is  absorbed  in  the  process  of  evaporation 
(page  85),  the  more  heat  there  is  available,  the  more 
rapid  will  be  the  evaporation. 

Evaporation  must  not  be  confused  with  boiling.  Heat 
is  absorbed  in  both  processes ;  but  boiling  takes  place  only 
at  a  definite  temperature  and  goes  on  inside  the  liquid. 

If  the  water  surface  is  large  and  the  temperature  high, 
there  is  a  large  amount  of  evaporation  and  the  water  rapidly 
rises  into  the  air.  In  the  tropics  the  evaporation  from  the 


MOISTURE    IN   THE  AIR 


101 


water  surface^mounts  to  perhaps  eight  feet  per  year.  This 
means  that  the  energy  of  the  sun  evaporates  about  five  hundred 
pounds  of  water  from  every  square  foot  of  the  surface  every 
year.  In  the  polar  latitudes  the  amount 
of  evaporation  is  perhaps  a  tenth  of  that 
in  the  tropics. 

From  every  water  surface  on  the  globe, 
however,  a  large  amount  of  water  is 
evaporated  each  year. 


BY  RAPID  EVAPO- 
RATION 


Effect  of  Temperature  on  the  Capacity 
of  the  Air  to  Hold  Moisture.  —  Experi- 
ment 37.  —  Take  a  liter  flask  and  put  into  it 
just  sufficient  water  to  make  a  thin  film  on  the 
inside  of  the  flask  when  shaken  around.  Now 
warm  the  flask  gently,  never  bringing  its  tem- 
perature near  to  the  boiling  point,  until  the 
water  disappears  from  the  inside  and  the  flask 
appears  to  be  perfectly  dry.  Having  tightly 
corked  the  flask,  allow  it  to  cool.  The  flask 
appears  dry  when  warm  and  on  account  of  having  been  corked 
tightly  no  moisture  could  have  entered  it.  The  air  in  the  flask 
was  perfectly  transparent  both  before  and  after  heating.  The  film 
of  water  around  the  inside  of  the  flask  was  taken  up  by  the  air 
when  it  was  warmed  but  the  moisture  reappeared  when  the  flask 
was  cooled. 

Experiment  38.  —  Fill  a  bright  tin  dish  or  glass  beaker  with  ice 
water  and  after  carefully  wiping  the  outside  allow  it  to  stand  for 
some  time  in  a  warm  room.  Can  water  go  through  the  sides  of 
the  dish?  Does  the  outside  of  the  dish  remain  dry?  If  water 
collects  upon  it,  from  where  does  the  water  come?  See  if  the  same 
results  will  follow  if  the  water  within  the  dish  is  as  warm  as  or 
warmer  than  the  air  in  the  room. 

Experiment  39.  —  Partially  fill  a  dish  or  beaker  like  that  in  the 
previous  experiment  with  water  having  a  temperature  a  little 
warmer  than  that  of  the  room.  Gradually  add  pieces  of  ice,  con- 


102     THE   ATMOSPHERE   AND    ITS   SERVICE    TO   MAN 

tinually  stirring  with  a  chemical  thermometer.  Note  the  tem- 
perature at  which  a  mist  begins  to  appear  upon  the  outside  of  the 
dish.  When  the  mist  has  appeared,  add  no  more  ice  but  stir  until 
the  mist  begins  to  disappear.  Note  this  temperature.  Take  the 
average  of  these  two  temperatures.  This  average  is  probably 
the  temperature  at  which  the  mist  really  began  to  form.  This 
temperature  is  called  the  dew  point. 

When  we  wish  to  dry  clothes,  we  place  them  in  a  warm 
room  or  in  the  sunshine.  Soon  we  find  that  the  water  has 
left  the  clothes.  It  must  have  gone  into  the  air.  It  would 
thus  appear  that  when  the  temperature  of  the  air  is  raised, 
it  has  the  capacity  of  taking  up  more  moisture  than  when  it 
is  cold.  This  was  seen  in  Experiment  37.  Both  Experi- 
ments 38  and  39  showed  that  when  air  is  sufficiently  cooled, 
it  begins  to  deposit  moisture.  Experiment  39  showed  the 
temperature  at  which  the  deposition  began.  This  was 
the  dew  point  for  that  time  and  place. 

This  property  that  air  has  of  taking  up  a  large  amount 
of  moisture  when  heated  and  of  giving  it  out  when  cooled 
is  the  cause  of  our  clouds  and  rain. 

Humidity.  —  The  condition  of  the  air  as  regards  the 
moisture  it  holds  is  called  its  humidity.  The  amount  of 
vapor  present  in  the  air  is  spoken  of  as  its  absolute  humidity. 
The  amount  of  vapor  in  the  air  as  compared  with  the  amount 
the  air  would  contain  if  it  had  all  it  could  hold  is  known  as 
its  relative  humidity.  For  example,  air  at  80°  F.  is  capable 
of  holding  almost  11  grains  of  water  vapor  per  cubic  foot. 
Suppose  it  actually  contains  6  grains  of  water  vapor  per 
cubic  foot.  It  will  be  loaded  then  with  about  -fr,  or  a  little 
more  than  |  of  the  moisture  it  would  contain  if  it  were 
saturated  (that  is,  had  all  the  moisture  it  could  hold).  This 
fraction  represents  the  relative  humidity  of  the  atmosphere. 


HUMIDITY 


103 


By  determining  the  dew  point  as  was  done  in  Experiment  39 
and  comparing  this  with  tables  which  have  been  prepared 
by  meteorologists  from  many  observations,  relative  humidity 
can  always  be  approximately  determined.  An  instrument 


STRATO-CUMULUS  CLOUDS 
Typical  low  level  clouds,  indicating  showers. 

for  determining  the  relative  humidity  of  the  air  is  called  a 
hygrometer  (Figure  50). 

To  be  considered  moist,  air  must  contain  at  least  more 
than  half  the  amount  of  moisture  it  is  capable  of  carrying. 
If  air  contains  much  more  than  half  the  moisture  it  can  carry, 
its  humidity  is  said  to  be  high.  When  air  which  has  a  high 
humidity  is  cooled  it  soon  reaches  a  point  of  temperature 
where  it  is  saturated  (the  dew  point).  If  the  temperature 
falls  below  this  point,  the  air  must  deposit  some  of  its  mois- 


104    THE   ATMOSPHERE   AND   ITS   SERVICE   TO   MAN 


ture.     It  is  important  not  to  think  of  the  dew  point  as  a 
fixed  point  of  temperature,  like  that  of  freezing  or  boiling. 
The  dew  point  depends  not  only  upon 
the   temperature    of    the   air  but   also 
upon  the  amount  of  vapor  in  the  air. 

Condensation  of  Moisture  of  the  Air. 
—  Moisture  of  the  air  may  condense 
into  little  droplets  high  above  the 
earth's  surface,  making  clouds.  If 
these  droplets  form  near  the  surface  of 
the  earth,  the  cloud  of  moisture  is 
called  fog.  If  it  collects  on  objects  on 
or  near  the  ground,  it  is  called  dew. 
When  droplets  in  the  clouds  become  so 
large  that  they  are  too  heavy  to  remain 
suspended  in  the  air,  they  fall  as  rain. 
Rain  and  dew  can  form  only  when  the 
dew  point  is  higher  than  the  freezing 
point.  When  the  dew  point  falls  below 
the  freezing  point,  moisture  of  the 
atmosphere  condenses  as  snow,  sleet,  or 
frost.  Thus  a  fall  of  snow  on  a  moun- 
tain is  sometimes  accompanied  by  rain 
FIGURE  50.— AN  HY-  in  the  valley. 

GBOMETER 

Cooling  by  Evaporation.  —  Experi- 
ment 40.  —  Mark  with  a  rubber  band  the  height  of  the  water  col- 
umn in  an  air  thermometer  (Figure  51).  Let  fall  a  few  drops  of 
ether  or  alcohol  on  the  bulb,  and  notice  the  change  in  the  height 
of  the  column.  Place  a  little  ether  on  the  back  of  the  hand.  What 
kind  of  sensation  does  it  give  ?  (Be  careful  to  use  only  a  few  drops 
of  ether,  as  it  is  bad  to  breathe  it  too  freely.) 


COOLING  BY   EVAPORATION 


105 


When  the  ether  was  dropped  on  the  air  thermometer 
bulb  it  evaporated  and  the  water  column  rose  just  as  it  did 


FOQ 

A  low  cloud  formed  near  the  surface  of  the  earth. 

in  Experiment  27.  Ether  is  one  of  a  number  of  liquids, 
such  as  gasoline  and  alcohol,  that  evaporate  more  rapidly 
than  water.  The  more  rapidly  a  liquid  evaporates,  the 
more  rapidly  it  takes  up  heat  from  its 
surroundings.  That  is  why  ether  feels 
colder  to  the  hand  than  water.  In  many 
places,  at  the  present  time,  advantage  is 
taken  of  rapid  evaporation  in  the  con- 
struction of  ice  and  cold-storage  plants. 

The  canvas  desert  water-bag  (Figure 
52)  illustrates  a  simple  application  of  the 
principle  of  cooling  by  evaporation.  The 
water  seeps  very  slowly  through  the  bag, 
and  the  evaporation  of  this  seeping  water 
absorbs  the  heat  from  the  water  in  the  bag  and  keeps 
it  cool  enough  to  refresh  the  thirsty  traveler.  Nature 


FIGURE  51 


106     THE   ATMOSPHERE   AND   ITS   SERVICE    TO   MAN 


FIGURE  52.  —  DESERT 
WATER  BAG 


provides   for   keeping   the   human    body    and    the    bodies 

of  some  other  animals  at  the  right  temperature  by  this 
process  of  evaporation.  The 
warmer  the  healthy  body  gets 
the  more  it  perspires,  and  the 
evaporation  of  the  perspiration 
keeps  down  the  temperature.  In 
case  of  fever,  the  pores  of  the 
body  close  up,  perspiration  ceases, 
and  the  temperature  immediately 
rises.  The  physician  often  has  to 
use  ice  packs  to  do  the  work  of 
normal  evaporation  until  perspira- 
tion resumes. 

Plants  are  also  kept  cool  by  the 

evaporation  of  water  which  exudes  from  their  leaves.     This 

is  called  transpiration. 

Humidity  and  Comfort.  —  The  humidity  of  the  air  has 
much  to  do  with  our  bodily  comfort.  In  quiet  warm  air, 
nearly  saturated  with  moisture,  the  perspiration  cannot 
readily  evaporate  and  cool  the  body.  Thus  a  temperature 
of  80°  F.  with  a  high  relative  humidity  may  be  more  un- 
comfortable than  a  temperature  of  95°  F.  with  a  low  relative 
humidity.  On  a  humid  day  the  perspiration  that  evap- 
orates brings  the  air  that  is  near  the  body  closer  to  the 
saturation  point,  and  we  fan  ourselves  to  move  it  away 
and  to  allow  the  less  moist  air  to  take  its  place.  Any  breeze 
gives  relief  because  it  keeps  changing  the  air  around  the 
body.  An  electric  fan,  although  it  in  no  way  cools  the  air, 
helps  evaporate  the  perspiration  by  keeping  the  air  in  mo- 
tion. Crowded  rooms  often  become  "  close  "  because  of  a 


HUMIDITY  AND  COMFORT 


107 


layer  of  densely  humid  air  around  the  crowd  that  results 
from  the  moisture  of  the  breath  and  the  evaporation  of 
perspiration.  Such  rooms  may  often  be  rendered  quite 
comfortable  by  opening  more  windows  or  by  starting  an 
electric  fan,  even  when  there  is  no  way  of  lowering  the 
temperature  of  the  atmosphere. 

In  cold  weather  when  the  temperature  of  the  body  is 
considerably  higher  than  that  of  the  surrounding  atmos- 
phere, moist  air  chills  us.  This  is  because  moist  air  is  a 
better  conductor  of  heat  than  dry  air  and  readily  absorbs 
heat  from  the  body. 

The  air  in  most  living  rooms  in  winter  is  too  dry.  Since 
the  air  in  the  room  has  been  heated  it  is  capable  of  holding 
more  moisture  than  the 
outdoor  air.  Unless  water 
is  supplied  to  it,  its  rela- 
tive humidity  is  much 
lower  than  that  of  the 
air  outside.  In  some 
heated  rooms  in  winter 
the  air  is  really  drier 
than  the  air  over  the 
deserts.  In  this  dry  air 
the  perspiration  evapo- 
rates very  rapidly  and 
makes  us  cold  even 

though  the  temperature  of  the  room  is  high.  This  hot, 
dry  air  is  injurious  to  the  eyes,  irritating  to  the  nerves, 
harmful  to  the  membranes  of  the  nose  and  throat,  and  con- 
ducive to  colds.  Such  air  dries  the  moisture  out  of  the  glue 
in  the  furniture,  often  warps  woodwork,  and  tends  to  shrivel 
up  everything  in  the  room. 


FIGURE  53. — HOMEMADE  HUMIDIFIER 


108     THE   ATMOSPHERE   AND    ITS   SERVICE    TO    MAN 

In  the  interest,  therefore,  of  the  conservation  of  health, 
as  well  as  of  fuel  and  of  furniture,  open  vessels  of  water 
(humidifiers)  should  be  kept  on  stoves,  radiators,  or  regis- 
ters, in  order  to  keep  the  air  of  living  rooms  moist.  Hang- 
ing up  cloths,  the  ends  of  which  are  in  pails  of  water,  will 
serve  the  purpose  even  better,  because  they  increase  the 
surface  from  which  evaporation  takes  place  and  thus  furnish 
more  water  to  the  air  in  less  time.  (Figure  53.)  There  are 
many  patented  devices  for  humidifying,  but  the  principle  on 
which  all  of  them  are  constructed  is  the  same  as  that  of  the 
homemade  humidifier.  A  temperature  of  between  65°  F. 
and  70°  F.  will  make  a  room  comfortable  if  there  is  sufficient 
moisture  in  the  air. 

Weight  of  Air.  —  Experiment  41.  —Into  a  five-pint  bottle  insert 
a  tightly  fitting  rubber  stopper  through  which  a  glass  tube  extends. 
To  the  outer  end  of  the  glass  tube  tightly  fit  a  thick- 
walled  rubber  tube  of  sufficient  length  for  the  attach- 
ment of  an  air  pump.  Put  a  Hoffman's  screw  upon  the 
rubber  tube.  (Figure  54.)  See  that  all  connections  are 
air-tight.  Weigh  carefully  the  apparatus  as  thus 
arranged.  Now  attach  the  rubber  tube  to  an  air  pump 
and  extract  the  air  from  the  bottle.  When  all  the  air 
FIGURE  54  t'ia*r  can  ^e  exhausted  has  been  removed,  close  the 
rubber  tube  tightly  with  the  Hoffman's  screw  and  weigh 
again.  Unclamp  the  Hoffman's  screw  and  allow  the  air  to  enter 
the  bottle.  The  weight  should  be  now  the  same  as  at  first.  Or, 
instead  of  weighing  a  bottle  of  air,  weigh  an  incandescent  light  bulb. 
Make  a  hole  in  it  with  a  blowpipe  and  weigh  again.  Is  the  weight 
now  the  same  as  before  ? 

We  have  found  by  the  previous  experiment  that  air  has 
weight.  With  the  apparatus  used  it  was  impossible  to 
tell  exactly  the  weight  of  the  air  extracted  or  to  determine 
the  weight  of  a  definite  volume  of  the  air.  If  we  had  been 


AIR  AS  AFFECTED   BY   HEAT  AND  COLD         109 

able  to  do  this,  we  should  have  found  that  on  an  average  day, 
at  sea  level,  the  weight  of  a  liter,  a  little  more  than  a  quart, 
of  air,  is  about  1.2  grams.  Twelve  cu.  ft.  weigh  about  one 
pound.  The  air  extends  to  so  great  a  height  that  although 
very  light,  the  weight  of  so  great  a  mass  of  it  is  enormous. 

Expansion  of  Air  when  Heated.  —  Air  expands  Very 
much  when  heated,  as  was  seen  in  Experiment  18.  It  is 
found  that  if  air  at  freezing  is  heated  to  the  temperature 
of  boiling  water,  it  will  expand  about  T*T  of  its  volume.  The 
force  with  which  air  expands  is  so  great  that  sometimes 
when  buildings  are  on  fire  and  there  is  no  opening  for  the 
confined  air  to  escape,  the  walls  are  blown  out  or  the  roof 
blown  off  by  the  expansion  of  the  hot  air,  and  great  injury 
is  done  to  those  fighting  the  fire.  That  air  expands  upon 
being  heated  is  readily  seen  when  an  air-filled  toy  balloon 
is  brought  from  the  cold  outer  air  &%£§> 

into  a  hot  room,  —  the  covering       ^  --  ii"  —  *t 
begins  at  once  to  tighten  and  the 
balloon  to  swell. 


Weight  of  Air  as  Affected  by 

Heat  and  Cold.  —  Experiment  42.—  FIGURE  55 

Take  two  open  flasks  of  nearly  the 

same  weight  and  capacity  and  balance  in  as  nearly  a  vertical 
position  as  possible  at  the  ends  of  the  arms  of  a  beam  balance. 
Bring  the  flame  of  a  Bunsen  burner  to  the  upper  side  of  the  bulb 
of  one  of  the  flasks  so  that  the  hot  air  currents  that  are  generated 
will  have  no  upward  push  on  the  flask.  (Figure  55.)  Do  not 
allow  the  hot  air  to  get  under  the  flask.  What  is  the  effect? 

As  the  previous  experiment  shows,  and  as  we  should 
expect  from  the  fact  that  air  has  been  found  to  expand 
when  heated,  hot  air  is  lighter  than  cold  air.  A  liter  of 
air  at  freezing  under  ordinary  pressure  weighs  about  1.293 


110     THE   ATMOSPHERE   AND    ITS   SERVICE    TO    MAN 


grams,  but  at  the  temperature  of  boiling  water  it  weighs 
only  about  .946  grams.  So  a  volume  of  cold  air,  being 
heavier,  will  exert  more  pressure  at  the  surface  of  the 
earth  than  an  equal  volume  of  hot  air. 

As  air  is  a  gas  whose  particles  can  move  freely  among 
themselves  we  should  expect  that  a  heavier  column  of  cold 

air  would  sink  down  and 
distribute  itself  along 
the  surface  under  sur- 
rounding lighter  air, 
just  as  a  column  of 
water  falls  when  its 
supports  are  withdrawn 
and  forces  up  the  lighter 
air  which  surrounds  it. 

A  similar  action  is 
seen  when  water  is 
poured  upon  oil  :  the 
water  sinks  to  the  bot- 
tom and  forces  the  oil 

to  rise.  Thus  if  air  is 
heated  at  any  place,  WC 

sh°uld  6XP6ct  that  there 

would  be  a  rising  current 
of  hot  air  and  a  current  of  colder  air  creeping  in  to  take 
its  place.  The  winds  of  the  earth  are  due  to  this  property 
of  air.  It  is  this  tendency  of  heated  air  to  rise  that  makes 
hot-air  furnaces  useful  for  heating  houses  (Figure  56). 
Valleys  are  generally  colder  than  the  surrounding  hill- 
sides, so  that  delicate  crops  can  be  grown  successfully 
on  the  hillsides  although  those  in  the  valley  may  be  frost- 
bitten. 


FIGURE  56.—  HOT-AIR  FURNACE 
Cold  air  presses  in  from  the  outside  and 


AIR  AS  AFFECTED  BY   HEAT  AND   COLD         111 


FIGURE  57 


Experiment  43.  —  Use  a  convection  apparatus  or  take  a  tight  chalk 
box  and  in  two  places  on  the  top  punch  holes  in  a  circle  not  quite 
as  large  as  the  bottom  of  a  lamp  chimney.  Place  a  small  lighted 
candle  at  the  center  of  one  of  the  circles  of  holes 
and  a  lamp  chimney,  tightly  sealed  to  the  box, 
about  each  circle.  Hold  a  smoking  piece  of  paper 
above  the  chimney  which  does  not  inclose  the 
candle.  (If  a  pane  of  glass  is  put  into  one  of  the 
vertical  sides  of  the 'box,  better  observations  can 
be  made.)  (Figure  57.)  What  happens?  Put 
out  the  candle  and  carefully  heat  the  chimney 
with  a  Bunsen  burner.  Is  there  the  same  action 
as  before  ?  Why  is  it  that  sparks  rise  from  a  fire  ? 
What  is  meant  by  the  draft  of  a  stove  ?  Why  in 
order  to  ventilate  a  room  is  it  best  to  open  a  window  at  the  top  and 
bottom  ? 

The  refrigerator  illustrates  the  effect  of  temperature  upon 
the  circulation  of  air  (Figure  58).  The  coldest  air  in  the  re- 
frigerator is  nearest  the  ice.  This  being  heaviest  naturally 
falls.  The  farther  away  from  the  ice  it  gets  the  warmer  and 

therefore  the  lighter  it  be- 
comes. The  falling  current 
of  cold  air  pushes  the 
warmer  air  up  through  the 
compartments  on  the  op- 
posite side  and  back  to 
the  ice  again,  thus  making 
a  continuous  circulation. 

It  is  not  generally  recog- 
nized that  an  electric  fan 
may  be  made  just  as  use- 
ful in  winter  as  in  summer. 
The  warm  air  in  a  room 
tends  to  rise  to  the  upper 


FIGURE  58.  —  REFRIGERATOR 

Diagram  illustrating  circulation  of  air 

when  the  doors  are  closed. 


112     THE   ATMOSPHERE    AND    ITS   SERVICE    TO   MAN 

part  of  the  room.  A  fan  placed  as  near  the  ceiling  as 
possible  will  force  this  warm  air  down  to  a  lower  level,  and 
in  this  way  make  all  parts  of  the  room  more  nearly  uniform 
in  temperature.  This  often  proves  an  effective  remedy  for 
cold  floors.  In  winter  the  air  near  windowpanes  is  often 
reduced  below  its  dew  point  and  films  of  ice  form  inside 
the  panes.  This  can  be  prevented  by  using  a  fan  to  keep 
a  fresh  supply  of  warm  air  moving  across  the  glass.  Most 
merchants  have  learned  to  apply  this  principle  in  keeping 
their  display  windows  clear  in  severe  weather. 

Ventilation.  —  The  movement  of  air  caused  by  its  heat- 
ing and  cooling  provides  a  means  for  ventilating  rooms  and 
buildings  in  winter.  In  warm  weather  we  do  not  have  to 
be  persuaded  to  keep  our  windows  open ;  but  when  winter 
comes,  many  people  become  careless  about  ventilating  their 
houses.  Health  requires  that  a  person  have  pure,  normally 
moist  air  to  breathe.  Sleeping  rooms  as  well  as  living 
rooms  must  be  constantly  supplied  with  outdoor  air.  The 
old  notion  that  night  air  was  harmful  is  contrary  to  the 
truth.  Fresh  air  day  and  night  is  essential  to  the  main- 
tenance of  health. 

Several  ways  have  been  devised  for  ventilating  large 
buildings  and  for  maintaining  proper  air  conditions,  but 
these  require  mechanical  means  for  driving  or  for  draw- 
ing the  air  into  the  building,  and  are  not  suitable  for 
dwellings. 

Houses  heated  by  hot-air  furnaces  in  which  the  cold  air 
flue  is  properly  cared  for  (Figure  56)  need  only  a  provision 
for  the  exit  of  hot,  stale  air.  An  open  grate  or  fireplace  in 
which  there  is  a  fire,  or  a  window  in  each  room  opened  slightly 
at  the  top  will  accomplish  this. 


VENTILATION 


113 


Houses  heated  by  steam  or  by  hot  water  sometimes  have 
special  arrangements  for  ventilating  (Figure  44).  In  some 
houses  the  radiators  are  placed  in  open  air  ducts  beneath  the 
floor.  The  fresh  air  enters  these  ducts  from  outdoors,  is 
warmed  as  it  passes  the  radiators,  and  rises  through  registers 
in  the  floor  to  warm  the  rooms.  The  cold  air  from  the  out- 
side keeps  pushing  the  warmed  air  up  out  of  the  ducts  and 
flowing  in  to  take  its  place.  Thus  a  continuous  circulation 
is  maintained  over  the  radiators  into  the  rooms.  The  same 
arrangements  must  be  made  for  the  exit  of  stale,  hot  air  as 
are  made  when  the  hot  air  furnace  is  used. 

Many  houses,  however,  cannot  be  ventilated  except 
through  the  windows  and  doors.  It  is  most  important 
to  learn  how  this  may  be  done  effectively.  One  simple 
method  is  to  cut  a  narrow  board  into  a  length  that  exactly 
equals  the  width  of  the  window  sash. 
Raise  the  lower  sash,  fit  the  board  into 
the  running  groove,  and  close  the  sash 
down  on  it.  This  leaves  an  open  space 
between  the  upper  and  the  lower  sash 
through  which  fresh  air  may  enter.  If 
the  upper  sash  be  pulled  down  to  leave 
an  opening  of  an  inch  or  so  at  the  top, 
an  exit  for  the  stale  air  is  provided. 

According  to  another  method,  a  board 
ten  or  twelve  inches  wide  is  cut  just  long 

,  .,       .      .1        «  ,1        FIGURE  59. — ADJUST- 

enough  to  reach  across  the  inside  ot  the      ABLE  VENTILATOR 
casement.     This  board  is  placed  length- 
wise on  the  inside  sill  with  its  ends  fastened  to  the  sides  of 
the  casement.     When  the  lower  sash  is  raised,  the  board  de- 
flects the  current  of  cold  air  upward  so  as  to  prevent  a  direct 
draft.     In  this  case  the  opening  between  the  sashes  serves 


114     THE   ATMOSPHERE   AND    ITS   SERVICE    TO   MAN 

as  an  exit  for  the  stale  air,  and  the  upper  sash  does  not  have 
to  be  lowered.  In  severe  weather  this  is  more  successful 
than  the  first  method.  An  adjustable  ventilator  of  this 
kind  is  shown  in  Figure  59. 

But  the  cloth  screen  is  probably  the  most  successful 
means  of  steady  ventilation  in  severe  weather.  For  houses 
that  have  only  casement  windows  it  is  about  the  only  method. 
Make  a  screen  frame  that  fits  snugly  into  the  casement. 
Cut  a  piece  of  muslin  to  fit  the  frame  and  tack  it  on  just  as 
you  would  wire  screening,  being  sure  to  stretch  the  muslin 
tight  as  you  put  it  on  the  frame.  With  this  in  place,  the 
casement  window  may  be  opened  wide  in  the  most  severe 
weather  without  any  danger  of  direct  drafts  but  with  assur- 
ance of  fresh  air  supply.  The  cloth  screen  may  be  adapted 
to  the  sash  window,  and  it  is  especially  useful  on  stormy 
nights  because  it  makes  it  possible  to  keep  a  sleeping  room 
window  wide  open  all  night. 

Whatever  method  of  ventilation  is  used,  the  windows  and 
doors  should  be  opened  once  or  twice  every  day  so  that  cold 
fresh  air  may  blow  in  and  flush  out  the  stale  air  of  the  rooms. 
Fresh  air  and  sunlight  are  man's  cheapest  doctors. 

Pressure  of  the  Atmosphere.  —  Experiment  44.— If  a  tin  can 
with  a  tightly  fitting  screw  cap  can  be  easily  procured,  boil  a  little 
water  in  it,  having  the  screw  cap  open  so  that  the  steam  can  readily 
escape.  While  the  water  is  still  strongly  boiling,  quickly  re- 
move the  can  from  the  heat  and  tighten  the  cap.  •  Be  sure  not  to 
tighten  the  cap  before  removing  the  can  entirely  from  the  heat. 
Set  the  tin  thus  closed  upon  the  desk  and  observe.  What  hap- 
pens as  the  steam  condenses?  Why? 

Experiment  45.  —  By  means  of  an 
air  pump  exhaust  the  air  from  a  pair  of 
Magdeburg  hemispheres.  (Figure  60.) 
Now  try  to  pull  the  hemispheres  apart.  FIGURE  60 


PRESSURE   OF   THE   ATMOSPHERE 


115 


FIGURE  61 


FIGURE  62 


It  cannot  be  done  as  easily  as    before  the  air  was  exhausted. 
Why? 

Experiment  46.  —  Fill  a  glass  tumbler  even  full  of  water  and 
press  upon  it  a  piece  of  writing  paper.  (Figure  61.)  Be  sure  that 
the  paper  fits  smoothly  to  the  rim  of  the  tumbler. 
Take  the  tumbler  by  its  base  and  carefully  invert 
it  over  a  pan.  Does  the  water  fall  out?  If  not, 
why  not?  While  the  tumbler  is  in  the  inverted 
position,  insert  the  point  of  a  pencil  between  the 
paper  and  the  rim  of  the  tumbler.  What  happens? 
Experiment  47.  —  Fill  a  bottle  with  clean  water 

and  fit  it  tightly  with  a  rubber  stopper  having  two 
holes  in  it.  Plug  one  of  the  holes  tightly  with  a  glass 
tube  one  end  of  which  has  been  closed  by  heating  in 
a  Bunsen  burner.  Through  the  other  hole  put  an 
open  glass  tube  10  to  15  cm.  long.  See  that  both 
tubes  fit  tightly  in  the  stopper  and  that  £he  stopper 
fits  tightly  in  the  bottle.  (Figure  62.)  Now  attempt 
to  "suck"  the  water  out  of  the  bottle  through  the 
open  tube.  Does  it  come  out  freely?  Pull  out  the  glass  plug. 
Does  it  come  out  any  better?  If  so,  why? 

Anything  that  has  weight  must  exert  pressure  upon  the 
surface  upon  which  it  rests.  The  air  has  been  found  to  have 
weight,  and  therefore  it  must  exert  pressure  at  the  surface 
of  the  earth.  It  is  a  gas;  and  since  the  particles  of  a  gas 
easily  move  over  one  another,  this  pressure  must  be  exerted 
equally  in  all  directions. 

We  do  not  feel  the  pressure  of  the  atmosphere  because  the 
pressure  inside  us  balances  the  pressure  from  without.  If 
two  eggshells,  with  their  contents  removed  —  one  of  them 
with  the  holes  left  in  it,  and  the  other  completely  sealed  — 
should  be  sunk  to  a  considerable  depth  in  water,  which  one 
would  be  crushed  by  the  pressure  of  the  water,  and  which 
would  not  ?  This  illustrates  why  objects  on  the  surface  of 
the  earth  are  not  crushed  by  the  pressure  of  the  air. 


116     THE   ATMOSPHERE   AND    ITS   SERVICE    TO   MAN 

In  the  preceding  experiments  atmospheric  pressure  ac- 
counted for  the  various  things  that  happened.  When  the 
steam  in  the  can  cooled,  it  condensed  and  occupied  less 
space.  The  pressure  of  the  atmosphere  from  the  outside, 
therefore,  pushed  the  sides  inward.  With  the  atmospheric 
pressure  lessened  inside  the  Magdeburg  hemispheres,  the 
full  atmospheric  pressure  on  the  outside  held  them  together. 
The  inverted  glass  kept  the  atmosphere  from  pressing  down 
on  the  surface  of  the  water  immediately  under  it.  The  up- 
ward pressure  of  the  atmosphere  on  the  paper  was  greater 
than  the  downward  pressure  of  the  water.  When  you 
withdrew  air  from  the  glass  tube,  the  pressure  of  the  at- 
mosphere on  the  surface  of  the  water  forced  the  water  up 
into  the  tube  to  take  the  place  of  the  air  that  had  escaped. 

Variation  in  pressure  due  to  heating  and  cooling  of  air 
explains  circulation  and  drafts.  A  column  of  cold  air  is 
denser  and  therefore  heavier  than  a  corresponding  column 
of  warm  air.  The  cold  air,  therefore,  presses  the  warm 
air  up,  and  takes  its  place  below. 

Measuring  Atmospheric  Pressure.  —  Experiment  48.  - 
(Teacher's  Experiment.)  — Take  a  thick- walled  glass  tube  of  about 
%  cm.  bore  and  80  cm.  length.  Close  it  at  one  end.  Fill  the  tube 
with  mercury.  (Be  sure  to  place  the  closed  end  of  the  tube  in  a 
large  vessel  so  as  not  to  waste  the  mercury  if  you  spill  it.)  Place 
the  thumb  tightly  over  the  open  end  of  the  tube  and  invert  it  in 
a  vessel  of  mercury.  If  you  are  at  or  near  sea  level,  the  mercury 
column  will  drop  to  a  height  of  about  75  cm.  (about  30  inches) 
and  will  stand  there.  This  is  known  as  Torricelli's  Experiment, 
because  Torricelli  first  performed  it  and  explained  it. 

The  space  above  the  mercury  is  without  air,  and  there- 
fore no  atmospheric  pressure  is  exerted  at  the  top  of  the 
column  of  mercury.  The  column  of  mercury  is  pressing 


MACHINES  THAT  MAKE   USE   OF  AIR  PRESSURE     117 

down  on  the  surface  of  the  mercury  in  the  vessel.  The 
atmosphere  is  also  pressing  down  on  the  surface  of  the  mer- 
cury in  the  vessel.  The  one  pressure  balances  the  other. 

It  makes  no  difference  what  the  diameter  of  the  column  of 
mercury  is,  it  will  stand  at  just  the  same  height.  If  then  we 
weigh  a  column  of  mercury  an  inch  square  at  the  base  and 
thirty  inches  tall,  we  can  find  what  the  approximate  pressure 
bf  the  earth's  atmosphere  is  on  every  square  inch  of  the  earth's 
surface  at  sea  level.  Such  a  column  weighs  about  fifteen 
pounds.  Therefore  the  pressure  of  the  atmosphere  is  about 
fifteen  pounds  to  the  square  inch  at  sea  level; 

Experiment  49.  —  (Teacher's  Experiment.)  — Take  a  thick- walled 
glass  tube  of  about  £  cm.  bore  and  about  80  cm.  length  and  slip 
tightly  over  the  end  of  it  about  10  cm.  of  a  thick- 
walled   flexible  rubber  tube  30   cm.   in   length. 
Firmly  secure  the  rubber  tube  to  the  glass  tube 
by  winding  tightly  around  them  many  turns  of 
string,  making  it  impossible  for  the  rubber  tube 
to  slip  or  admit  air.     Completely  close  the  rubber 
tube  with  a  Hoffman's  screw  just  beyond  the         FIGURE  63 
place  where  it  leaves  the  glass  tube.    Placing  this 
closed  end  in  a  large  dish  so  as  not  to  waste  any  mercury,  fill  the 
glass  tube  with  mercury.    Place  the  thumb  over  the  open  end  of 
the  tube  and  invert  it  in  a  cup  of  mercury.     If  the  connections 
were  made  tight,  the  mercury  will  not  fall  far  below  the  end  of  the 
glass  tube.    The  air  pressure  keeps  the  mercury  up.    This  is  a 
simple  form  of  barometer. 

While  the  tube  is  still  standing  in  the  mercury  cup  take  another 
glass  tube  similar  to  the  first  and  attach  it  to  the  open  end  of  the 
rubber  tube  in  the  same  way  as  the  first  was  attached.  Place 
the  free  end  of  this  tube  in  a  dish  of  colored  water  and  gradually 
open  the  Hoffman's  screw.  (Figure  63.)  The  water  rises  in  the  tube. 
Why?  What  is  meant  by  sucking  water  up  a  tube? 

Machines  that  Make  Use  of  Air  Pressure.  —  Lift  Pump. 
—  The  ordinary  lift  pump  (Figure  64)  is  a  machine  which 


118     THE   ATMOSPHERE   AND    ITS   SERVICE    TO   MAN 


utilizes  air  pressure  for  "  lifting  "  water.  When  the  piston 
of  the  pump  is  raised  from  the  bottom  of  the  cylinder  a 
partial  vacuum  is  created  in  the  cylinder.  The  air  pressure 
on  the  water  in  the  cistern  forces  the  water  up  the  pipe  and 
through  the  valve  B  into  the  cylinder.  When  the  piston 
descends  the  valve  B  in  the  bottom  of  the  cylinder  is  closed 
by  the  weight  of  the  water  and  the  valve  A  in  the  piston 
opens  allowing  the  water  to  flow  through' 
to  the  upper  side  of  the  piston.  As  the 
piston  is  once  more  raised  the  valve  A 
closes  and  the  water  above  the  piston  is 
lifted  and  flows  out  the  spout.  Air  pres- 
sure again  forces  more  water  up  the  pipe 
and  through  the  valve  B  into  the 
cylinder.  The  water  continues  to  rise 
into  the  cylinder  and  to  be  lifted  out  as 
long  as  the  pump  is  worked. 

Lift  pumps  were  in  use  for  2000  years 
before  any  one  successfully  explained 
their  operation.  Galileo  observed  that 
in  the  best  lift  pumps  the  water  could 
not  be  made  to  rise  higher  than  32  feet, 
but  he  died  without*  being  able  to  ex- 
plain why.  When  Torricelli,  his  pupil  and  friend,  performed 
the  experiment  with  the  mercury  tube,  and  found  that  atmos- 
pheric pressure  would  support  a  column  of  mercury  about 
30  inches  high  in  a  vacuum,  he  explained  what  had  puzzled 
Galileo.  Since  mercury  is  about  thirteen  and  one-half 
times  as  heavy  as  water,  the  pressure  of  the  atmosphere 
would  support  a  column  of  water  thirteen  and  one-half 
times  as  high  as  the  column  of  mercury.  In  a  perfect 
vacuum,  therefore,  the  pressure  of  the  atmosphere  would 


FIGURE  64.  —  DIA- 
GRAM OF  A  LIFT 
PUMP 


THE   SIPHON 


119 


FIGURE  65 


support  a  column  of  water  about  34  feet  high.  But  since  it 
is  impossible  to  create  a  perfect  vacuum  with  the  piston  and 
valves,  water  never  rises  as  high  as  this  in 
a  lift  pump.  In  practice  the  average  limit  is 
about  27  feet. 

The  Siphon.  —  Experiment  50.  —  Fill  an  eight- 
ounce  bottle  with  clean  water  and  fit  it  tightly 
with  a  two-holed  rubber  stopper.     Through  one  of 
the   holes  in  the  stopper  insert  a  tightly  fitting 
glass  tube,  which  reaches  nearly  to  the  bottom  of 
the  bottle  and  extends  an  inch  or  two  above  the  stopper.     Attach 
to  this  glass  tube  a  clean  rubber  tube  which  is  long  enough  to  reach 
below  the  bottom  of  the  bottle.     Fit  a  sealed  glass  tube  so  that  it 

can  be  readily  in- 
serted in  the  open 
hole  of  the  stopper. 
(Figure  65.) 

"  Suck  "  water 
out  of  the  end  of 
the  rubber  tube 
hanging  below  the 
bottom  qf  the 
bottle.  As  soon  as 
the  water  begins  to 
flow,  withdraw  the 
mouth  without  rais- 
ing the  tube.  The 
water  will  still  con- 
tinue to  flow.  In- 
sert the  sealed  glass 
tube  in  the  open 
hole  of  the  stopper. 
The  water  stops 
flowing.  Pull  out 

A  GREAT  SIPHON  IN  THE  Los  ANOELES  the  glass  plug.    The 

AQUEDUCT  water     begins     to 


120     THE    ATMOSPHERE    AND    ITS   SERVICE    TO   MAN 

flow  again.  If  the  water,  once  started,  is  allowed  to  flow,  it  will 
empty  the  bottle  to  the  end  of  the  glass  tube.  Any  bent  tube 
arranged  in  this  way,  with  one  arm  longer  than  the  other,  is  called 
a  siphon. 

In  Experiment  50,  the  water  in  the  siphon  was  pressed 
outward  from  the  bottle  by  atmospheric  pressure  minus  the 
weight  of  the  column  of  water  in  the  short  arm.  It  was 
pressed  toward  the  inside  of  the  bottle  by  atmospheric  pres- 
sure minus  the  weight  of  the  column  of  water  in  the  long 
arm.  The  atmospheric  pressure  was  practically  the  same  in 
both  cases,  but  the  weight  of  the  water  column  in  the  short 
arm  was  less  than  that  of  the  water  column  in  the  long 
arm.  The  pressure  acting  outward  was  therefore  greater 
than  that  acting  inward  and  the  water  flowed  out  of  the 
bottle.  The  siphon  continued  to  flow  as  long  as  the  in- 
equality of  pressure  was  maintained.  When  the  atmospheric 
pressure  was  shut  off  by  the  insertion  of  the  sealed  glass 
tube,  the  water  of  course  stopped  flowing. 

Vacuum  Cleaners.  —  Experiment  61.  —  Allow  a  beam  of  light 
to  enter  a  darkened  room  through  a  small  hole  in  a  curtain.  Note 
as  carefully  as  you  can  the  different  things  hi  the  air  that  the 
beam  of  light  reveals. 

In  the  preceding  experiment  we  observed  that  the  air 
contained  something  more  than  the  gases  and  moisture 
which  we  have  learned  are  in  it.  There  are  many  solid 
particles  floating  in  the  air.  There  were  little  shreds  of 
cloth  and  paper,  pieces  of  dust  and  soot,  and  many  other 
things.  The  beam  of  light,  however,  did  not  reveal  every- 
thing that  was  floating  in  the  air.  There  were  many  living 
organisms,  tiny  plants  (bacteria),  too  small  to  be  seen  except 
by  the  aid  of  a  high-power  microscope. 

These  minute  living  things  are  scattered  all  through  the 


VACUUM  CLEANERS 


121 


air,  sometimes  living  on  dust  particles  and  sometimes  un- 
attached to  anything.  Only  a  few  of  the  bacteria  are  harm- 
ful, and  they  are  usually  not  very  abundant.  Sunlight 
kills  most  of  them  in  a  short  time,  but  moisture  and  dark- 
ness furnish  conditions  favorable  for  them.  Thev  are 


Courtesy  o/  Elgin  Sales  Corporation 
A  MODERN  STREET  SWEEPER 

The  left  end  is  the  forward  end.  This  machine  sprinkles,  sweeps,  and 
collects  the  sweepings.  The  operator  is  working  the  lever  which 
empties  the  machine. 

particularly  abundant  in  the  dust  of  the  street  and  wherever 
foul  refuse  accumulates.  When  they  get  into  a  house  they 
settle  and  multiply  rapidly  if  they  happen  to  light  upon  a 
warm,  moist  place  where  the  sunshine  is.  not  too  bright. 
Ordinary  dusting  and  sweeping  simply  scatter  them  about 
and  keep  them  floating  in  the  air  for  hours,  for  us  to 


122     THE   ATMOSPHERE   AND    ITS   SERVICE    TO   MAN 

breathe.  Carpet  sweepers  and  oiled  dust  cloths  do  much 
to  prevent  stirring  up  the  dust  and  bacteria,  but  vacuum 
cleaners  are  even  more  effective. 

The  vacuum  cleaner  is  a  device  to  utilize  air  pressure  for 
cleaning.  By  means  of  a  pump  or  a  rapidly  rotating  fan, 
the  air  in  the  machine  is  exhausted.  Atmospheric  pres- 
sure forces  the  air  up  through  the  mouth  of  the  machine, 
driving  the  dust  and  dirt  particles  with  it.  This  dust- 
laden  air  passes  into  a  closely  woven  bag,  which  sifts  out  and 
collects  most  of  the  dust.  By  using  this  machine  no  dust  is 
scattered  through  the  air  of  the  room. 

Vacuum  cleaners  have  also  been  invented  for  street 
cleaning,  but  outdoor  conditions  make  them  less  satisfactory 
than  vacuum  cleaners  for  the  household.  Most  cities  de- 
pend upon  washing  or  sweeping  to  keep  the  streets  clean. 
Where  sweepers  are  used,  they  should  always  be  preceded 
by  sprinklers  in  order  to  keep  down  as  much  of 
the  dust  as  possible. 

Decrease  of  Volume  Due  to  Pressure.  —  Experi- 
ment 52.  —  In  a  Marietta's  tube  (Figure  66)  cause 
about  a  centimeter  of  mercury  in  the  short  arm  to 
balance  the  same  amount  in  the  long  arm.  The 
pressure  inside  the  short  tube  will  then  be  equal  to 
that  outside  the  long  tube  and  will  be  that  of  the  air 
upon  the  day  of  the  experiment.  The  short  arm  will 
now  be  sealed  with  mercury  so  that  no  air  can  get  in 
or  out.  Pour  mercury  into  the  long  arm.  The  air 
in  the  short  arm  will  be  gradually  compressed  and  will 
occupy  less  and  less  space.  If  we  remember  that  the 
pressure  upon  the  air  in  the  short  arm  is  the  air  pres- 
sure of  the  day  plus  the  pressure  of  the  mercury 
column  in  the  long  arm  that  rises  above  the  mercury  level  in  the 
short  arm,  we  can  show  by  careful  measurement  that  the  volume  of 
the  air  decreases  just  as  the  pressure  increases. 


I 


VOLUME  AND  PRESSURE  123 

As  was  seen  in  Experiment  9,  the  volume  of  air  can  be 
very  much  decreased  by  pressure.  It  cannot  be  told  from 
this  experiment  whether  the  volume  of  the  gas  decreases 
as  the  pressure  increases  or  whether  it  decreases  much  more 
rapidly  when  first  pressed  upon  than  afterward.  This 
can  be  best  shown  by  the  use  of  the  Mariotte's  tube  as 
in  Experiment  52.  But  if  the  bicycle  pump  is  a  good  one, 
it  will  answer  the  question  of  the  rate  of  decrease  quite  ac- 
curately. It  is  found  that  the  volume  decreases  directly  as 
the  pressure  increases. 

Increase  of  Pressure  Due  to  Decrease  of  Volume. — When 
a  given  volume  of  air  is  compressed  it  exerts  more  pressure. 
If  air  is  compressed  to  one  third  its  original  space,  it  will  exert 
three  times  as  much  pressure  as  it  did  before.  When  the 
pressure  is  removed  it  regains  its  original  volume.  A 
puncture  in  an  inflated  automobile  tire  shows  how  rapidly 
and  forcibly  air  will  expand  from  its  greater  density  under 
pressure  to  the  density  of  the  surrounding  atmosphere. 
These  properties  of  compressibility  and  expansion  which  air 
has,  in  common  with  other  gases,  have  many  practical  ap- 
plications. One  of  the  most  familiar  applications  is  in  the 
air  pumps  of  garages.  Compressed  air  is  also  used  to  apply 
brakes  on  street  cars,  steam  engines,  and  railway  coaches. 
It  is  used  to  blow  whistles,  to  ventilate  mines  and  large 
buildings,  and  to  operate  heavy  hammers,  rock  drills,  and 
riveting  machines. 

The  force  pump  illustrates  a  use  of  compressed  air.  An 
"  air  cushion  "  is  used  to  deliver  a  steady  stream  of  water 
to  a  point  higher  than  the  mouth  of  the  pump.  In  the  force 
pump,  the  water  rises  into  the  cylinder  when  the  piston  is 
raised,  exactly  as  in  the  ordinary  lifting  pump.  The  piston 


124     THE    ATMOSPHERE    AND    ITS   SERVICE    TO   MAN 


has  no  valve,  and  so  when  it  descends  it  forces  the  water 
out  through  the  pipe  (E)  (Figure  67)  into  the  air  chamber 
(D),  thus  compressing  the  air 
in  it.  The  valve  (C)  keeps 
the  water  from  running  back 
when  the  piston  is  lifted. 
While  the  piston  is  ascend- 
ing, the  pressure  of  the  air 
cushion  (D)  forces  a  steady 
stream  through  the  pipe  (^4) 
to  the  tank  above. 

The  force  pump  is  some- 
times used  to  fill  tanks  in 
attics  of  farmhouses  so  as 
to  provide  private  water- 
systems.  The  principle  of 
the  force  pump  is  used  in 
the  more  complicated  pumps  for  water-works,  fire  engines, 
and  mines. 

Heat  Produced  by  Compression  and  Cooling  Produced  by 
Expansion.  —  Experiment  63.  —  Have  a  five-pint  glass  bottle  fitted 
with   a  two-hole   rubber  stopper.      Pass  through  the 
holes  in  the  stopper  a  chemical  or  air  thermometer  and 
a  short  glass  tube.    The  lower  end  of  the  glass  tube 
which  extends  into  the  bottle  should  be  kept  as  far  as 
possible  away  from  the  bulb  of  the  thermometer,  so 
that  when  the  air  is  exhausted  or  allowed  to  enter  the 
bottle  there  will  be  no  movement  of  the  air  near  the 
bulb  of  the  thermometer.     The  end  of  the  column  of 
the  thermometer  must  be  visible  above  the  stopper.    pIGT7RE  6g 
(Figure  68.) 

Attach  the  glass  tube  to  an  air  pump  by  means  of  a  thick-walled 
rubber  tube.  Note  the  temperature  of  the  thermometer  within 
the  bottle  and  also  of  the  air  outside.  Quickly  exhaust  the  air- 


FIGURE  67.  —  DIAGRAM  OF  A 
FOBCE  PUMP 


PRESSURE   AND   THE   BOILING  POINT  125 

from  the  bottle,  carefully  noting  the  action  of  the  thermometer. 
See  that  the  temperature  of  the  air  in  the  room  does  not  change 
during  the  experiment.  Allow  the  air  quickly  to  enter  the  bottle 
and  note  the  action  of  the  thermometer.  The  temperature  inside 
the  bottle  changes  as  the  air  is  quickly  exhausted,  or  as  it  is  allowed 
to  enter  the  bottle  again  and  thus  to  increase  the  density  of  the 
air  in  the  bottle. 

It  has  been  found  that  when  air  or  any  other  gas  expands, 
it  absorbs  heat  and  cools  its  surroundings ;  and  when  it  is 
compressed,  it  yields  heat  and  warms  its  surroundings. 
This  heating  and  cooling  by  changes  in  the  density  of  gas 
is  called  adiabatic  heating  or  cooling.  It  is  taken  advantage 
of  in  the  manufacture  of  liquid  air  and  is  the  same  principle 
which  is  utilized  in  cold-storage  plants.  This  property  of 
air  has  much  to  do  with  developing  our  wind  circulation  and 
storms. 

The  heating  effect  of  compressing  air  can  be  well  seen 
when  an  automobile  tire  is  filled.  No  matter  how  well  the 
piston  of  the  pump  may  be  oiled,  as  the  density  of  the  air 
in  the  tire  begins  to  increase,  the  pump  will  grow  warm 
rapidly.  This  rapid  heating  cannot  be  due  to  friction,  as 
the  pump  is  not  being  worked  any  more  swiftly  than  at 
first.  It  is  due  to  the  greater  compression  of  the  air.  As 
this  compression  increases,  the  heating  increases,  the  effect 
of  friction  in  a  well-oiled  pump. being  of  small  value. 

Pressure  and  the  Boiling  Point.  —  Experiment  54.  —  (Teach- 
er's Experiment.)  —  Fill  a  strong  500  cc.  round-bottomed  flask 
about  one  third  full  of  water.  Boil  the  water.  While  the 
water  is  briskly  boiling,  remove  the  flask  from  the  heat,  quickly 
close  its  mouth  with  a  rubber  stopper,  and  invert  it  in  a  ringstand. 
(Figure  69.)  (Be  sure  not  to  insert  the  stopper  until  the  flask  is 
fully  removed  from  the  heat.)  Pour  cold  water  upon  the  flask. 
The  water  will  again  begin  to  boil. 


126     THE   ATMOSPHERE   AND    ITS   SERVICE    TO   MAN 


FIGURE  69 


In  this  experiment  the  steam  was  condensed  by  the  sud- 
den lowering  of  the  temperature.  The  condensation  of  the 
steam  relieved  the  pressure  on 
the  surface  of  the  water,  and 
the  water  in  the  flask  began  to 
boil  again  although  it  had  be- 
come considerably  cooler  than 
when  it  was  first  boiled.  Thus 
it  appears  that  if  the  pressure 
on  the  surface  of  water  is  de- 
creased, the  water  will  boil  at 
a  lower  temperature.  Advan- 
tage is  taken  of  this  in  condens- 
ing milks  and  sirups.  The 
liquids  are  heated  under  hoods 
from  which  air  is  continuously 

exhausted.     The  water  is  thus  "boiled  away"  at  so  low 

a  temperature  that  there  is  no  danger  of   scorching  the 

sirup  or  the  milk. 
On     high     mountains 

where  the  air  pressure  is 

considerably  less  than  at 

sea  level,  water  boils  at 

less    than    100°    C.     In 

Denver   it   boils  at  95° 

C.;     in     the     City    of 

Mexico,  at   92°  C.;    in 

Quito,  Ecuador,  at  90° 

C.     Because  water  boils 

in  such  places  at  a  lower 

temperature,     it     takes 

longer  to  boil   food  Until  PKKSSUBE  COOKEB 


THE  MANUFACTURE   OF   ICE  127 

it  is  "done."  To  hasten  the  process  of  cooking  by  boiling 
in  high  altitudes,  pressure  cookers  are  often  used.  The 
high  pressure  developed  by  keeping  the  steam  imprisoned 
raises  the  boiling  point  of  the  water  within.  The  contents 
of  the  cooker  may  thus  be  brought  to  a  temperature  of 
170°  C.  or  even  more.  This  intense  heat  reduces  the  time 
of  cooking  and  thus  saves  fuel. 

The  Manufacture  of  Ice ;  Cold  Storage.  —  We  saw  in 
Experiment  53  that  when  air  was  compressed  it  gave  up 
heat  and  warmed  its  surroundings.  When  pressure  was 
removed,  the  air  absorbed  heat  and  cooled  its  surround- 
ings. Other  gases  act  in  the  same  way.  Water  vapor,  for 
example,  may  be  compressed  until  it  gives  up  so  much  heat 
that  it  returns  to  the  liquid  state. 

Ammonia  is  a  gas  that  at  ordinary  temperatures  is  easily 
condensed  by  pressure  into  a  liquid.  (This  liquid  must 
not  be  confused  with  the  aqua  ammonia  of  our  kitchens, 
which  is  simply  water  that  has  absorbed  ammonia  gas.) 
When  the  pressure  is  removed,  the  liquid  ammonia  quickly 
returns  to  the  gaseous  state,  and  in  so .  doing  it  absorbs 
much  heat. 

Figure  70  shows  the  essential  construction  of  an  ice 
plant.  The  pump  (A)  compresses  the  ammonia  gas  into 
the  pipes  at  (B).  The  pressure  condenses  the  gas  into 
liquid,  and  the  cold  running  water  absorbs  the  heat  given 
out  in  the  process.  The  liquid  thus  cooled  is  allowed  to 
run  very  slowly  through  the  valve  (C),  into  the  pipes  at 
(/)).  The  valves  in  the  pump  (A)  are  so  arranged  that 
while  the  pump  increases  the  pressure  in  the  pipes  at  (B) 
it  decreases  the  pressure  in  the  pipes  at  (D).  Because  of 
the  low  pressure  in  the  pipes  (D),  the  liquid  ammonia  evapo- 


128     THE   ATMOSPHERE   AND    ITS   SERVICE    TO   MAN 

rates ;  that  is,  returns  to  the  gaseous  state.  In  so  doing  it 
absorbs  heat  very  rapidly  from  its  surroundings  (page  105). 
The  gaseous  ammonia  returns  to  (A)  from  the  pipes  (D) 
because  of  the  exhaust  action  of  the  pump.  It  is  again 
compressed  into  the  pipes  at  ($).  Thus  the  action  con- 
tinues without  loss  of  ammonia. 

The  ammonia  pipes  pass  through  the  brine  into  which 
cans  of  water  have  been  lowered.  Brine  is  used  to  sur- 
round the  ice  cans  because  it  does  not  freeze  unless  its 


FIGURE  70.  —  DIAGRAM  SHOWING  ESSENTIAL  CONSTRUCTION  OF 
AN  ICE  PLANT 

temperature  is  reduced  many  degrees  below  the  tempera- 
ture at  which  pure  water  freezes.  The  evaporation  of  the 
ammonia  in  the  pipes  reduces  the  temperature  of  the  brine 
so  low  that  the  water  in  the  cans  is  frozen,  but  the  brine  re- 
mains liquid,  so  that  the  cans  may  be  easily  removed. 

In  cold  storage  plants  the  pipes  (D)  are  placed  in  the  cold 
storage  rooms  to  reduce  the  temperature  of  the  air  in  the 
rooms,  just  as  they  reduce  the  temperature  of  the  brine  in 
the  ice  plant. 

The  Barometer.  —  On  account  of  the  movements  of  the 
air  due  to  heating  and  cooling  and  to  other  causes,  the 


THE   BAROMETER  129 

pressure  of  the  atmosphere  at  'any  place  on  the  earth's 
surface  is  liable  to  change.  Since  measurement  of  atmos- 
pheric pressure  is  of  great  importance  in  the 
study  of  atmospheric  conditions,  it  is  necessary 
to  have  an  instrument  by  which  changes  in  pres- 
sure can  be  readily  measured.  An  instrument 
designed  for  this  purpose  is  called  a  barometer. 
There  are  two  kinds  of  barometers  in  common 
use,  the  mercurial  and  the  aneroid. 

If  the  tube  used  in  Torricelli's  Experiment 
(page  116)  is  fixed  in  an  upright  position,  and  the 
height  of  the  mercury  marked  from  time  to  time, 
it  will  be  found  that  the  height  of  the  mercury 
column  changes  slightly,  thus  indicating  greater 
or  less  atmospheric  pressure.  In  Torricelli's  Ex- 
periment, therefore,  we  had  a  mercurial  barometer 
in  rough  form. 

The  best  form  of  this  instrument  consists  of 
a  glass  tube  of  uniform  bore  about  eighty  centi- 
meters long  and  closed  at  one  end.  After  being 
carefully  filled  with  pure  mercury,  it  is  inverted 
in  a  cistern  of  mercury.  The  cistern  of  mercury 
has  a  sliding  bottom  easily  moved  up  and  down 
by  means  of  a  set  screw.  At  the  top  of  the 
cistern  there  is  a  short  ivory  peg.  The  lower 
end  of  the  ivory  peg  is  at  an  exactly  measured 
distance  from  the  bottom  of  a  scale.  The  scale 
is  placed  beside  a  slit  near  the  top  of  a  metallic 
tube  which  is  firmly  fastened  to  the  cistern  and 
surrounds  and  protects  the  glass  tube. 

When  it  is  desired  to  read  the  barometer,  the  ., 

,.  ,.  „  .  .         .  MERCURIAL 

sliding  bottom  or  the  cistern  is  raised  or  lowered  BAROMETER 


130     THE    ATMOSPHERE   AND    ITS   SERVICE    TO   MAN 


ANEROID  BAROMETER 


until  the  top  of  the  mercury  in  the  cistern  just  touches  the 
bottom  of  the  ivory  peg.     The  height  of  the  top  of  the 

mercury  column  is  then 
read  from  the  scale.  In 
order  to  determine  the 
height  with  great  preci- 
sion there  is  generally 
attached  to  the  metallic 
tube  a  sliding  vernier 
which  moves  in  a  slit. 

The  aneroid  barometer 
consists  in  general  of  a 
corrugated  metallic  box 
from  which  the  air  has 
been  partially  exhausted. 
Within  the  box  is  a  stiff  spring  so  that  the  pressure  of  the 
air  will  not  cause  it  to  collapse.  Attached  to  the  box  are 
levers  by  which  any 
change  in  the  volume  of 
the  box  will  be  multi- 
plied and  indicated  by 
a  pointer  arranged  to 
move  over  a  dial  with  a 
scale  upon  it. 

Instruments  called 
barographs  are  con- 
structed in  which  a  long 

lever     provided     with     a     This  is  arranged  so  as  to  record   the  air 
.        .  pressure  automatically  for  a  week  at  a 

pen  point  is  attached  to       time, 
the  anejoid  and  made  to 

record  on  a  cylinder  revolved  by  clockwork.     Thus  a  con- 
tinual record  is  made  of  barometric  readings. 


BAROGRAPH 


DETERMINATION   OF   HEIGHT   BY  BAROMETER      131 

Determination  of  Height  by  a  Barometer.  —  Experiment  65. 
—  Carry  an  aneroid  barometer  from  the  bottom  of  a  high  building 
to  the  top.  Note  the  reading  of  the  barometer  at  the  bottom 
and  again  at  the  top.  Why  is  the  barometer  lower  at  the  top  of 
the  building? 

As  the  pressure  of  air  at  any  surface  is  due  to  the  weight 
of  the  air  above  that  surface,  it  happens  that  as  we  go  up 
the  pressure  decreases,  since  there  is  a  continually  de- 
creasing weight  of  air  above.  If  the  rate  of  this  decrease 
is  determined,  then  it  is  possible  to  determine  the  elevation 
by  ascertaining  the  pressure. 

Although  the  height  of  the  barometer  is  continually  vary- 
ing with  the  changing  air  conditions,  yet  if  these  conditions 
remain  about  the  same,  it  may  roughly  be  estimated  that 
the  fall  of  TS  of  an  inch  in  the  height  of  the  mercury  column 
indicates  a  rise  of  about  57  feet,  and  that  the  fall  of  a  milli- 
meter indicates  a  rise  of  about  11  meters.  These  values 
are  fairly  reliable  for  elevations  less  than  a  thousand  feet, 
under  ordinary  temperatures  and  pressures. 

At  the  height  of  25  miles  the  barometric  column  would 
probably  not  be  more  than  ^  of  an  inch  high.  Several 
measurements  made  in  different  ways  indicate  that  the  air 
is  at  least  100-  miles  in  depth,  probably  more.  Nearly 
three  fourths  of  the  atmosphere,  however,  is  below  the  top 
of  the  highest  mountain.  The  highest  altitude  ever  reached 
by  man  was  about  7  miles. 

To  study  air  conditions  small  balloons  to  which  meteoro- 
logical instruments  are  attached  have  been  sent  to  a  height 
of  21  miles.  It  is  found  that  the  minimum  temperatures 
occur  at  a  height  of  from  6  to  10  miles.  Conditions  affect- 
ing weather,  however,  seem  to  extend  to  a  height  of  not 
much  over  3  miles. 


132     THE   ATMOSPHERE    AND    ITS   SERVICE    TO    MAN 

The  atmosphere,  of  course,  must  be  densest  at  its  lowest 
level  since  the  pressure  due  to  the  weight  of  the  air  is  greatest 
there.  The  farther  we  ascend  the  less  dense  the  air  becomes. 
This  is  the  chief  reason  why  people  from  a  lower  altitude 
"  get  out  of  breath  "  easily  when  they  go  to  a  higher  alti- 
tude. It  is  also  the  reason  why  balloons  and  airplanes 


OBSERVATION  WAR  BALLOONS 


can  ascend  only  to  a  limited  distance.  Since  the  gas  in  the 
balloon  is  less  dense  than  the  lower  atmosphere,  it  rises  to 
a  point  where  the  density  of  the  air  just  balances  the  aver- 
age density  of  the  balloon  and  its  burden. 


SUMMARY 


The  gaseous  envelope  of  the  earth  is  called  its  atmosphere. 
The  chief  gases  of  the  atmosphere  are  oxygen,  which  is 


SUMMARY  .  133 

necessary  for  animal  life;  nitrogen,  which  dilutes  the  oxy- 
gen; and  carbon  dioxide,  which  is  indispensable  to  plant 
life. 

Water  exposed  to  air  evaporates.  Through  this  process, 
the  atmosphere  always  contains  moisture.  Warm  air  has 
a  greater  capacity  for  moisture  than  cold  air.  The  property 
that  air  has  of  taking  up  a  large  amount  of  moisture  when 
heated  and  of  depositing  it  when  cooled  is  the  cause  of  dew, 
fog,  clouds,  rain,  frost,  snow,  and  sleet.  When  a  liquid 
evaporates  it  takes  up  heat  from  its  surroundings.  This 
principle  is  employed  by  man  in  ice  and  cold  storage  plants 
and  by  nature  in  evaporation  of  moisture  from  the  surfaces 
of  animals  and  plants.  Care  should  be  taken  in  winter  to 
keep  the  air  in  houses  supplied  with  sufficient  moisture. 

Air,  like  every  other  substance,  has  weight.  Air  expands 
as  it  is  heated,  and  so  warm  air  is  lighter  than  cold  air.  Since 
the  particles  of  air  or  any  other  gas  move  freely  over  one 
another,  cold  air  will  sink  and  force  up  warmer  air  that  sur- 
rounds it.  Hot  air  furnaces,  circulation  in  a  refrigerator, 
and  ventilation  of  houses  depend  on  this  principle. 

Since  anything  that  has  weight  exerts  pressure  on  the 
surface  on  which  it  rests,  air  exerts  pressure  at  the  surface 
of  the  earth,  which  amounts  to  about  15  pounds  to  the 
square  inch.  Lift  pumps,  siphons,  and  vacuum  cleaners 
are  among  the  mechanical  devices  that  make  use  of  air 
pressure. 

The  volume  of  air  decreases  directly  as  the  pressure  in- 
creases. When  a  given  volume  of  air  is  compressed,  it 
exerts  corresponding  outward  pressure.  This  principle  is 
applied  in  operating  brakes,  steam  whistles,  ventilating 
systems,  heavy  hammers,  and  force  pumps. 

When  air  or  any  other  gas  is  compressed  it  gives  out  heat 


134     THE   ATMOSPHERE   AND    ITS   SERVICE    TO   MAN 

and  increases  the  temperature  of  its  surroundings ;  when 
it  expands  it  absorbs  heat  and  lowers  the  temperature  of  its 
surroundings. 

The  greater  the  pressure  on  a  liquid  surface,  the  higher 
is  the  boiling  point ;  the  lower  the  pressure,  the  lower  the 
boiling  point.  This  principle,  along  with  the  principle  that 
a  substance  absorbs  heat  as  it  changes  from  a  liquid  to  a 
gaseous  state,  underlies  the  operation  of  cold  storage  and 
ice-manufacturing  plants. 

The  barometer  is  an  instrument  for  measuring  atmos- 
pheric pressure.  Since  atmospheric  pressure  decreases  with 
altitude,  a  barometer  may  be  used  to  measure  altitude. 

QUESTIONS 

What  are  the  characteristics  and  principal  uses  of  the  three  most 
abundant  gases  in  the  atmosphere? 

What  experiences  have  you  ever  had  which  show  that  hot  air 
will  hold  more  moisture  than  cold  air? 

How  have  you  ever  seen  cooling  by  evaporation  used  ? 

In  what  ways  does  the  moisture  in  the  atmosphere  affect  bodily 
comfort  ? 

How  can  it  be  shown  that  the  air  has  weight  and  exerts  pressure? 

What  effect  has  heat  upon  the  weight  and  volume  of  the  atmos- 
phere ? 

Suggest  several  methods  for  properly  ventilating  a  house. 

What  effect  has  pressure  upon  the  weight  and  volume  of  air? 

Explain  the  construction  of  three  machines  which  make  use  of 
atmospheric  pressure. 

In  what  way  do  compression  and  expansion  affect  the  tempera- 
ture of  a  gas? 

How  are  the  boiling  points  of  liquids  affected  by  pressure? 
What  practical  uses  are  made  of  this  principle  ? 

How  is  ice  manufactured  ? 

How  do  the  two  kinds  of  barometers  ordinarily  used  differ  in 
construction  ? 


CHAPTER  VI 


THE  WATEKS   OF   THE  EAETH 

Importance  of  Water.  —  Water  is  found  to  some  extent 
everywhere  on  the  earth's  surface.  It  is  necessary  to  the 
life  of  all  plants  and  animals  and  makes  up  a  large  part  of 
their  weight.  Man  may  live  without  food  for  a  few  weeks 
but  cannot  live  more  than  a  few  days  without  water.  The 
earth  has  been  likened  by  some  writers  to  a  water  engine, 
since  water  has  played  such  an  important  part  in  its  history. 

Composition  of  Water.  — Experiment 56.— (Teacher's  Experi- 
ment.)—  Place  a  small  handful  of  zinc  scraps  in  a  strong  wide- 
mouthed  bottle.  Fit  the 
bottle  with  a  two-holed  rub- 
ber stopper  having  a  thistle 
tube  extending  through  one 
hole  and  a  bent  delivery 
tube  through  the  other. 
The  thistle  tube  should 
reach  nearly  to  the  bottom 
of  the  bottle.  Connect  the 
delivery  tube  with  the  shelf 
of  a  pneumatic  trough  by  a 
rubber  tube.  Have  several 
inverted  8-oz.,  wide-mouthed  bottles  filled  with  water  on  the  shelf 
of  the  trough.  (Figure  71.)  Pour  enough  water  through  the 
thistle  tube  to  partly  cover  the  zinc  and  then  pour  on  commercial 
hydrochloric  acid  or  sulphuric  acid  diluted  1  to  10. 

Chemical  action  will  take  place  between  the  zinc  and  the  acid 
135 


FlOUBE    71 


136        THE  WATERS  OF  THE  EARTH 

and  hydrogen  will  be  freed.  Allow  the  gas  to  escape  for  several 
minutes,  so  as  to  rid  the  generating  bottle  of  the  air  in  it.  Collect 
several  bottles  full  of  the  hydrogen.  Keep  the  bottles  inverted. 
Examine  the  hydrogen  in  one  of  the  bottles.  Has  it  color  or  odor? 
Holding  the  mouth  downward  thrust  a  lighted  splinter  into  an- 
other bottle.  The  splinter  does  not  continue  to  burn  in  this  gas 
but  the  gas  itself  burns.  Place  another  bottle  mouth  up  on  the 
table  and  allow  it  to  stand  for  several  minutes.  Insert  a  lighted 
splinter.  Why  is  not  the  hydrogen  still  present? 

Draw  out  a  glass  tube  so  that  the  bore  will  be  about  as  large  as 
the  point  of  a  pencil  and  insert  it  in  the  rubber  delivery  tube.  Pour 
more  acid  into  the  bottle  and  after  this  has  been  working  for  several 
minutes  touch  a  lighted  match  to  the  glass  tip  of  the  rubber  delivery 
tube.  A  jet  of  burning  hydrogen  will  be  formed.  Hold  a  cold,  dry 
beaker  over  this  burning  jet.  Water  drops  will  collect  in  the  beaker. 
The  hydrogen  is  combining  with  the  oxygen  of  the  air  and  water  is 
being  formed. 

Pure  water  is  a  colorless,  odorless,  tasteless  liquid.  In 
Experiment  15  we  decomposed  water  by  the  electric  current 
and  found  it  to  be  composed  of  two  gases,  hydrogen  and 
oxygen.  In  Experiment  56  we  burned  hydrogen,  thus 
uniting  it  chemically  with  the  oxygen  of  the  air  and  forming 
water.  Oxygen  we  have  studied.  Hydrogen  is  a  colorless, 
odorless,  transparent  gas,  the  lightest  of  all  known  sub- 
stances. It  must  be  handled  carefully,  because  if  it  is  mixed 
with  oxygen  and  the  mixture  is  ignited,  a  violent  explosion 
results. 

Effects  of  Varying  Temperatures  on  Water.  —  We  have 
learned  that  water  evaporates  at  any  temperature  and  in  so 
doing  always  absorbs  heat  from  its  surroundings.  When  it 
condenses  it  gives  out  the  heat  absorbed  during  evaporation. 
When  water  at  ordinary  temperatures  is  heated  it  expands 
until  it  reaches  the  boiling  point.  At  this  temperature, 
the  change  of  water  from  liquid  to  vapor  goes  on  most 


EFFECT  OF  VARYING  TEMPERATURES  ON  WATER    137 

rapidly,  and  the  change  of  state  increases  its  volume  more 
than  1700  times.  It  is  this  stupendous  pressure  of  rapidly 
generating  water-vapor  that  is  "  harnessed  "  in  the  steam 
engine.  This  is  one  of  the  most  marvelous  manifestations 
of  the  energy  of  heat. 

Experiment  67.  —  Fill  a  flask  of  about  500  cc.  with  water.  Press 
into  the  mouth  of  the  flask  a  rubber  stopper  through  which  a  glass 
tube  about  30  cm.  long  extends.  The  tube  should  be  open  at  both 
ends  and  should  not  extend  into  the  flask  below  the  bottom  of  the 
cork.  When  the  cork  is  pressed  in,  the  water  will  be  forced  up 
into  'the  tube  for  several  centimeters.  See  that  the 
cork  is  tight  and  that  there  are  no  bubbles  of  air  in  the 
flask  or  tube. 

Now  place  the  flask  for  fifteen  or  twenty  minutes  in 
a  mixture  of  ice  and  water  (Figure  72)  and  carefully 
mark  with  a  rubber  band  the  point  at  which  the  water 
in  the  tube  comes  to  rest.     Take  the  flask  out  of  the 
freezing  mixture  and  notice  immediately  whether  the 
water  in  the  tube  rises  or  falls.     Continue  for  five  or    FIGURE  72 
ten  minutes  to  notice  the  action 'of  the  water  in  the 
tube.    The  volume  of  the  water  is  not  the  least  when  it  is  at  the 
temperature  of  melting  ice,  32°  F.,  but  when  it  is  a  little  above 
this  temperature. 

Experiment  58.  —  Put  a  piece  of  ice  in  water.  What  part  of  its 
volume  sinks  below  the  surface  of  the  water?  Is  it  heavier  or  lighter 
than  water?  From  Experiment  32  do  you  conclude  that  cold 
water  is  heavier  or  lighter  than  warm  water? 

When  water  at  ordinary  temperatures  is  cooled  it  contracts 
and  grows  denser.  It  continues  to  do  this  until  the  whole 
body  of  water  reaches  a  temperature  of  about  4°  C.  Here 
a  remarkable  change  takes  place ;  for  as  water  is  cooled  below/ 
this  point  it  expands.  This  expansion  goes  on  until  the 
liquid  turns  to  solid  at  0°  C. 

At  the  moment  water  solidifies  into  ice,  it  expands  with 


138        THE  WATERS  OF  THE  EARTH 

such  tremendous  force  that  it  exerts  a  pressure  of  more  than 
100  tons  to  the  square  foot.  No  wonder  it  bursts  water 
pipes,  splits  rocks  and  concrete  sidewalks,  and  heaves  the 
foundations  of  buildings  that  have  not  been  laid  below 
"  frost  line."  After  ice  has  once  formed,  it  again  begins 
to  contract  as  the  temperature  is  lowered,  but  it  never 
reaches  the  density  of  water.  i 

It  can   easily   be    seen   why   any  river  or  lake  or  other 
body  of  water  freezes  from  the  top  down.     Since  water  at 
the  freezing  point  is  less  dense  and  therefore 
lighter  than  slightly  warmer  water,  it  remains 
at  the  surface,  where  it  freezes.     Ice  is  even 
BOMB     BURST    lighter  than  water  at  the  freezing  point,  and 
BY  FREEZING    so  ft  floats.     As  soon  as  ice  has  formed  over 
the  surface,  it  acts  as  a  blanket,  allowing  the 
heat  to  escape  only  very  slowly  from  the  water  underneath. 
Thus  the  ice  increases  in  thickness  so   slowly  that  spring 
comes  before  a  deep  body  of  water  can  freeze  to  the  bottom ; 
and   so  fish  and  other  forms  of  water  life  never  become 
chilled  below  freezing  nor  suffer  serious  inconvenience. 

Ability  of  Water  to  Absorb  Heat.  —  We  have  already 
learned  that  it  takes  more  heat  to  raise  a  given  mass  of 
water  one  degree  of  temperature  than  to  cause  a  like  in- 
crease in  temperature  in  an  equal  mass  of  almost  any  other 
substance.  This  was  shown  in  Experiment  29.  When 
water  cools,  it  gives  out  the  heat  it  took  up  when  its  tempera- 
ture was  raised.  A  pound  of  water  in  cooling  one  degree 
gives  out  about  as  much  heat  as  a  pound  of  iron  in  cooling 
nine  degrees.  It  is  for  this  reason  that  hot-water  furnaces 
are  so  efficient,  that  hot-water  bags  are  used  to  keep  people 
warm,  and  that  farmers  sometimes  in  winter  carry  down 


WATER  AS  A  SOLVENT  139 

tubs  of  water  to  keep  their  cellars  above  the  freezing  point. 
For  the  same  reason  orange  groves  are  often  irrigated  when 
a  heavy  frost  threatens. 

This  capacity  for  holding  heat  makes  bodies  of  water  warm 
up  slowly  in  the  summer  and  cool  off  slowly  as  winter 
approaches.  If  we  bear  in  mind  that  practically  the 
entire  mass  of  a  body  of  water  must  reach  a  uniform  tem- 
perature of  4°  C.  before  it  begins  to  freeze  at  the  surface, 
this  slowness  of  water  to  change  temperature  will  explain 
why  large  bodies  of  water  so  seldom  freeze  except 
around  the  shallow  edges. 

Water  as  a  Solvent.  —  Experiment  69.  —  Put  a 
little  salt  into  water  in  a  clean  beaker  or  drinking  glass, 
and  stir.  The  solid  entirely  disappears.  Taste  the 
water.  Has  the  salt  affected  the  water  in  any  way? 
Pour  out  three  fourths  of  the  water  and  taste  again. 
Is  there  any  difference  between  the  saltiness  of  the 
upper  portion  and  the  lower  portion  of  the  water? 

Experiment  60.  —  (Teacher's  Experiment.)  —  Fill  a 
tall  bottle  with  water  colored  with  blue  litmus.  By  FIGUKE  73 
means  of  a  long  thistle  tube,  slowly  pour  a  little 
sulphuric  acid  into  the  bottom  of  the  bottle.  (Figure  73.)  Allow 
the  bottle  to  stand  undisturbed  and  note  the  gradual  change  in 
color  of  the  litmus,  showing  that  the  heavier  acid  is  mixing,  or 
diffusing,  upward  through  the  water. 

Experiments  59  and  60  show  that  when  substances  are 
dissolved  in  water  they  tend  to  mix  thoroughly  with  the 
water  and  to  form  a  uniform  solution.  When  we  mix 
water,  lemon  juice,  and  sugar  together  to  make  lemonade, 
the  solution  has  a  uniform  taste  throughout.  Neither  the 
solid  nor  the  liquid  tend  to  separate  out  of  the  solution 
nor  to  accumulate  in  any  one  part  of  it.  As  a  result 
of  this  characteristic  of  solutions,  the  water  of  the  whole 


140        THE  WATERS  OF  THE  EARTH 

ocean    from    top    to    bottom    is    practically    uniform    in 
composition. 

Water  is  the  greatest  of  all  solvents.  It  dissolves  to  a 
greater  or  less  extent  almost  all  substances  with  which  it 
comes  in  contact.  There  are,  however,  substances  which  it 
dissolves  but  slightly  if  at  all.  When  it  is  necessary  to  get 
these  substances  into  solution,  other  solvents  must  be  used. 


MONTEZUMA'S  WELL 

A  famous  water  hole  due  to  the  dissolving  power  of  water  on  rock- 
forming  substances. 

Gasoline,  for  example,  dissolves  grease ;  turpentine  dissolves 
fresh  paint,  and  alcohol  dissolves  grass  stain. 

Experiment  61.  —  Fill  a  small  beaker  with  fresh  water.  Heat  it 
slowly.  Bubbles  collect  on  the  bottom  and  sides.  When  the 
water  becomes  cold  these  bubbles  do  not  disappear  immediately. 
If  these  were  bubbles  of  water  vapor,  they  would  condense  to  water 
when  the  temperature  was  lowered.  What  are  they?  Where 
did  they  come  from? 

We  have  learned  that  all  air  has  water  vapor  diffused 
through  it.  Experiment  61  showed  that  there  was  also 


FREEZING  MIXTURES  141 

air  in  water.  All  water  exposed  to  air  has  air  dissolved  in 
it.  It  is  upon  this  air  in  solution  that  fishes  depend  for  the 
oxygen  they  need.  But  while  air  may  hold  moisture,  and 
water  may  hold  air,  Experiments  37  and  61  show  an  impor- 
tant point  of  difference  between  the  capacity  of  air  for  water 
and  of  water  for  air.  We  learned  that  when  air  is  heated 
it  is  capable  of  holding  more  water  vapor.  But  when 
water  is  heated,  it  is  capable  of  holding  less  air. 

Experiment  62.  —  Stir  salt,  a  little  at  a  time,  into  a  test  tube  of 
water  which  is  no  warmer  than  the  temperature  of  the  room. 
Gradually  increase  the  salt  until  the  water  will  absorb  no  more, 
and  a  little  of  the  salt  settles  at  the  bottom  of  the  test  tube.  Now 
heat  the  solution.  What  happens  to  the  salt  at  the  bottom  of 
the  test  tube  ?  Set  the  test  tube  containing  the  solution  aside 
to  cool.  Does  any  of  the  salt  reappear  in  solid  form? 

If  we  put  as  much  of  a  solid  substance  into  a  liquid  as  the 
liquid  will  dissolve,  we  have  a  saturated  solution.  If  any 
more  of  the  solid  is  added,  it  will  remain  undissolved. 
As  the  temperature  of  water  increases,  it  can  hold  more 
solid  matter  in  solution.  If  a  liquid  at  a  certain  tempera- 
ture is  saturated  with  a  solid  and  then  is  reduced  to  a 
lower  temperature,  it  will,  under  ordinary  circumstances, 
deposit  some  of  the  solid.  What  similar  thing  happens  in 
the  atmosphere? 

Freezing  Mixtures.—  Experiment  63.  —  Place  some  chopped 
ice  in  a  beaker,  and  test  the  temperature.  Add  a  generous  amount 
of  salt  and  test  the  temperature  again.  Has  there  been  a  fall  of 
temperature? 

Salt  and  some  other  substances  tend  to  absorb  water  and 
to  form  a  solution  whenever  it  is  possible.  On  a  damp  day 
salt  sticks  in  the  salt-shaker.  This  simply  indicates  that 
salt  has  absorbed  moisture  from  the  atmosphere. 


142        THE  WATERS  OF  THE  EARTH 

It  is  found  that  when  salt  or  any  other  solid  is  in  solution 
in  water,  more  heat  is  required  to  boil  the  solution  and  a 
lower  temperature  to  freeze  it  than  are  required  by  pure 
water.  A  saturated  salt  solution  freezes  only  at  -22°C. 
(-  7°  F.)  although  pure  water  freezes  at  0°  C.  The  freezing 
point  of  a  salt  solution  may,  therefore,  be  anywhere  from 
slightly  below  0°  C.  to  -22°  C.,  dependent  upon  the  strength 
of  the  solution.  Salt  placed  directly  upon  ice  will  cause  the 
ice  to  melt  and  form  a  solution  if  the  temperature  is  above 
-22°  C.  This  explains  why  salt  may  be  used  successfully 
to  melt  ice  on  porch  steps,  sidewalks,  and  car-track  switches. 

When  ice  is  placed  in  salt  water  it  takes  from  its  surround- 
ings the  heat  necessary  to  change  it  from  the  solid  to  the 
liquid  state  and  continues  to  do  this  until  the  freezing  point 
of  the  solution  is  reached.  It  thus  happens  that  the  tem- 
perature of  such  a  solution  may  become  much  lower  than  the 
freezing  point  of  water  and  yet  the  solution  remain  unfrozen. 
Most  substances  placed  in  such  a  solution  become  quickly 
frozen.  A  solution  of  this  kind  is  used  in  freezing  ice-cream. 
About  three  parts  of  snow  or  ice  to  one  part  of  salt  are  the 
best  proportions  to  use. 

Substances  in  Suspension  and  in  Solution  in  Water. — 

Experiment  64. —  Into  a  glass  of  clear  water  stir  a  half  teaspoonful 
of  sand  and  fine  dust.  Cover  the  glass  and  set  it  aside.  After 
an  hour  or  so  examine  the  glass  and  see  if  any  of  the  sand  and 
dust  has  settled  to  the  bottom.  If  so,  stir  it  up  again.  What 
happens? 

It  was  found  in  Experiment  64  that  water  is  able  to  hold 
solids  in  suspension  and  that  the  finer  the  solid  particles 
the  longer  they  stay  suspended.  It  was  also  found  that 
when  the  water  was  in  motion  (stirred)  it  held  more  and 
larger  particles. 


SUSPENSION   AND   SOLUTION 


143 


SETTLING  BASINS  OF  THE  ST.  Louis  WATER  PLANT 

Muddy  river  water  is  pumped  into  these  basins  and  is  allowed  to  stand 
until  it  loses  its  heavier  sediment  (Experiment  64).  The  combined 
capacity  of  these  basins  is  245,000,000  gallons. 

Experiment  66.  —  Add  some  salt  to  the  contents  of  the  glass 
used  in  the  preceding  experiment.  Arrange  a  glass  funnel  with  a 
filter  paper  hi  it,  as  shown  hi  Figure  74.  Pour  the  contents  of  the 
glass  into  the  funnel  and  collect  the  water 
that  runs  through  the  filter  paper.  Do  the 
sand  and  dust  run  through?  Put  a  little  of 
the  filtered  water  hi  a  watch  crystal  or  in  a 
shallow  vessel  and  allow  it  to  evaporate.  Did 
the  salt  in  solution  come  through  the  filter 
paper? 

Filters  of  all  kinds  are  used  to  remove 
suspended  materials  from  water ;  but  as 
was  shown  in  Experiment  65,  the  sub-  FIGURE  74 


144 


THE   WATERS   OF   THE    EARTH 


stances  in  solution  cannot  be  removed  in  this  way.  When 
dirty  surface  water  seeps  down  through  thick  enough  beds 
of  sand  and  porous  rock,  it  is  cleansed  of  its  dirt ;  but  it 
does  not  lose  by  this  filtering  process  any  of  the  substances 
it  held  in  solution.  On  the  contrary,  it  may  have  dissolved 
substances  from  the  rocks  through  which  it  filtered.  In 

this  way  "  soft  " 
rain  water  may  be- 
come hard  water  or 
mineral  water  before 
it  reaches  the  surface 
again  in  springs  or 
wells. 

When  water  has 
absorbed  carbon  di- 
oxide it  is  able  to 
dissolve  limestone 
and  it  then  becomes 
hard.  When  water 
of  this  kind  is  boiled 
or  evaporated  the 
carbon  dioxide 
escapes  and  the  lime 
deposits,  thus  ren- 
dering the  water  soft.  Such  water  is  called  temporarily 
hard  water.  Boiler  and  teakettle  scale  are  deposits  from 
temporarily  hard  water.  Permanently  hard  water  cannot 
be  softened  by  boiling. 

Emulsions.  —  Experiment  66.  —  Put  a  few  drops  of  kerosene  or 
other  oil  into  a  test  tube  hah0  full  of  water.  Since  the  oil  is  lighter 
than  the  water  it  rises  to  the  surface.  Shake  the  test  tube  vig- 
orously. Does  the  oil  mix  with  the  water?  Set  the  test  tube 


A  LIMESTONE  CAVE 
A  cavern  dissolved  out  by  water.     Hard 


rater 


trickling  in  and  evaporating  has  formed  the 
columns. 


EMULSIONS  145 

aside  and  allow  it  to  stand  for  a  short  time.     Does  the  oil  remain 
mixed  with  the  water? 

Put  oil  and  water  into  another  test  tube  and  add  finely  shaved 
soap  or  a  little  soap  solution.  Shake  the  test  tube  vigorously  and 
set  it  aside  for  a  while.  Does  the  oil  now  rise  to  the  surface  ? 

When  the  oil  was  shaken  with  the  water,  it  divided  into 
minute  globules  scattered  through  the  water,  giving  the 
mixture  a  milky  appearance.  The  oil  soon  separated  from  the 
water  and  floated  on  top  of  the  water  just  as  it  did  before 
the  test  tube  was  shaken.  When  soap  was  added  and 
shaken  with  the  oil  and  water,  the  globules  remained  in 
suspension  and  did  not  separate  from  the  water  when  it 
was  set  aside  for  a  while.  A  suspension  of  this  kind  is 
called  an  emulsion. 

It  is  the  power  of  emulsifying  oil  and  grease  that  makes 
soap  so  useful  as  a  cleansing  agent.  Water  will  not  dis- 
solve grease;  but  when  soap  solution  is  rubbed  on  oily  or 
greasy  materials,  the  oil  or  grease  is  converted  into  little 
droplets,  each  surrounded  by  a  film  of  soap  solution.  These, 
with  the  little  particles  of  dust  and  dirt  which  they  contain, 
are  easily  removed  by  rinsing  with  water.  The  natural 
oils  of  the  skin  accumulate  impurities  from  various  sources. 
Since  water  will  not  dissolve  this  oil,  soap  is  an  essential  in 
bathing. 

If  soap  is  used  in  hard  water,  a  sticky  white  substance  is 
formed  which  will  not  dissolve  in  water.  This  gummy 
substance  is  a  chemical  combination  of  soap  with  the  mineral 
salts  dissolved  in  the  water.  The  soap  combines  chemically 
with  these  mineral  salts  until  all  the  salts  are  broken  up  and 
the  water  is  softened.  Until  enough  soap  is  dissolved  to 
soften  the  water,  an  emulsion  will  not  form.  This  results  in 
such  a  great  waste  of  soap  that  cheaper  substances  such 


146 


THE    WATERS   OF   THE    EARTH 


as  borax  or  washing  soda  are  often  used  to  soften  water  for 
laundry  work.  These  substances  combine  chemically  with 
the  mineral  salts  in  solution  and  leave  the  water  free  to 
form  an  emulsion  with  soap. 

Pressure  in  Water.  —  Experiment  67.— Tie  a  piece  of  thin  sheet 
rubber  (dentist's  rubber)  tightly  over  the  mouth  of  a  small,  short 
thistle  tube.  Attach  tightly  to  the  neck  of  the  thistle  tube  a 
flexible  rubber  tube  about  two  feet  long.  Bend  a  glass  tube  into 
the  shape  of  a  U,  making  one  arm  slightly  longer  than  the  other. 
Put  colored  water  into  the  U-tube  until  it  stands  about  two  inches 
high  in  each  arm  of  the  tube.  Fasten  a  meter 
stick  in  a  perpendicular  position  and  tie  the 
U-tube  to  it  so  that  the  long  arm  lies  along  the 
scale.  Attach  the  open  end  of  the  rubber  tube 
to  the  short  arm  of  the  U-tube.  When  you 
press  on  the  rubber  sheet  at  the  mouth  of  the 
thistle  tube,  the  water  rises  in  the  long  arm  of 
the  U-tube.  You  have  made  a  simple  pressure 
gauge.  (Figure  75.) 

Nearly  fill  a  battery  jar  with  water.  Slowly 
push  the  thistle  tube  down  into  the  water  and 
notice  the  action  of  the  column  of  water  in  the 
U-tube.  How  does  increasing  depth  affect  pres- 
sure? Being  careful  to  keep  the  center  of  the 
rubber  diaphragm  at  the  same  depth,  face  it  up,  down,  and  side- 
ways. Does  the  pressure  in  different  directions  vary  at  the  same 
depth?  Hold  the  thistle  tube  at  equal  depth  hi  the  battery  jar 
and  in  a  pail  or  tub  of  water.  Does  the  greater  volume  of  water  in 
the  pail  make  any  difference  in  the  pressure  at  the  same  depth? 

Pressure  in  water  varies  directly  as  the  depth,  and  at  the 
same  depth  pressure  is  equal  in  all  directions.  At  a  given 
depth  the  volume  of  the  water  makes  no  difference  with  the 
pressure.  The  pressure  would  be  no  greater  in  a  lake  six 
inches  below  the  surface  than  at  the  same  depth  in  the 
battery  jar.  For  that  reason,  the  pressure  on  a  water  main 


FIGURE  75 


PRESSURE  IN  WATER 


147 


issuing  from  the  bottom  of  a  standpipe  would  be  just  as 
great  as  from  a  reservoir  of  great  area,  provided  the  depth 
of  water  in  each  is  the  same.  It  follows,  therefore,  that  the 
bottom  of  a  standpipe  supporting  a  fifty-foot  column  of 
water  would  have  to  be  just  as  strong  as  the  bottom  of  a 
dam  holding  back  the  waters  of  a  lake  fifty  feet  deep.  Of 
course  in  a  heavier  liquid  than  water,  pressure  would  in- 
crease more  rapidly  with  the  depth ;  and  in  a  lighter  liquid, 
less  rapidly. 

Another  important  property  of  water  and  of  all  other 
liquids  is  that  they  transmit  pressure  equally  in  all  direc- 
tions. If  a  bottle  be  com- 
pletely filled  with  water  and 
pressure  be  suddenly  applied 
to  the  stopper,  the  trans- 
mitted pressure  may  break 
the  sides  of  the  bottle.  If 
the  area  of  the  face  of  the 
cork  that  pressed  upon  the 
surface  of  the  water  in  the 

bottle  were  one    square  inch        FIGURE  76.  —  HYDRAULIC  PRESS 

and  the  pressure  applied  to 

the  cork  were  twenty-five  pounds,  .then  the  twenty-five 
pounds  of  pressure  on  the  square  inch  of  water  surface 
would  be  conveyed  to  every  square  inch  of  the  inner 
surface  of  the  bottle. 

This  property  liquids  have  of  transmitting  pressure 
equally  in  all  directions  has  many  practical  applications. 
One  of  the  most  common  is  the  hydraulic  press  (Figure  76) . 
In  this  machine  a  relatively  small  amount  of  pressure  on 
the  small  piston  achieves  tremendous  results  at  the  large 
piston.  Suppose,  for  example,  the  area  of  the  face  of  the 


148        THE  WATERS  OF  THE  EARTH 

small  piston  is  one  square  inch  and  the  area  of  the  face 
of  the  large  piston  is  100  square  inches.  If  a  pressure  of  25 
pounds  were  exerted  downward  on  the  small  piston,  an 
equal  pressure  would  be  exerted  upward  on  every  square 
inch  of  the  face  of  the  large  piston.  Thus  25  pounds  pres- 
sure on  the  small  piston  would  cause  an  upward  pressure  of 
2500  pounds  on  the  large  piston. 

In  the  operation  of  this  press,  the  large  piston  would 
rise  only  one  hundredth  as  far  as  the  small  piston  descended. 
If  the  small  piston  descended  a  foot,  the  large  piston  would 
rise  one  hundredth  of  a  foot.  In  other  words,  the  pressure 
on  either  piston  times  the  distance  it  travels  equals  the 
pressure  on  the  other  piston  multiplied  by  the  distance  it 
travels. 

The  enormous  force  that  can  be  exerted  by  the  hydraulic 
press  is  used  in  baling  cotton  and  paper,  in  punching  holes 
through  steel  plates,  in  extracting  oil  from  seeds,  in  lifting 
huge  machines,  and  in  many  other  devices  where  immense 
pressure  is  needed. 

Buoyancy  of  Water.  —  Experiment  68.  — Prepare  a  block  of 
wood  having  dimensions  of  6x4x4  cm.  Bore  a  hole  in  one 
end  of  the  block  and  fill  it  with  sufficient  lead  so  that  it  will 
readily  sink  in  water.  Tightly  close  the  hole  containing  the  lead 
and  dip  the  block  in  melted  paraffin  to  make  it  entirely  waterproof. 
Carefully  measure  the  block  and  compute  its  volume  in  cubic 
centimeters. 

Drive  a  small  tack  into  the  center  of  one  of  the  smaller  faces 
of  the  block.  Attach  a  thread  to  the  tack  and  lower  the  block 
into  a  cylinder  graduated  to  cubic  centimeters.  Pour  into  the 
cylinder  more  than  enough  water  to  cover  the  block.  Read  on 
the  cylinder  scale  the  combined  volume  of  the  block  and  the  water. 
Pull  the  block  out  of  the  water.  Read  on  the  scale  the  volume  of 
the  water  left  in  the  cylinder.  Does  the  difference  between  the 
two  readings  equal  the  computed  volume  of  the  block? 


BUOYANCY   OF  WATER 


149 


From  this  experiment  we  learn  that  a  body  submerged  in 
water  displaces  a  volume  of  water  equal  to  its  own  volume. 
A  cubic  block  measuring  exactly  96  cubic  centimeters 
would  displace  96  cubic  centimeters  of  water. 

Experiment  69.  —  Attach  the  block  prepared  for  the  previous 
experiment  to  a  spring  balance  with  a  scale  reading  in  grams,  and 
weigh  it.  Lower  the  block  suspended  from  the  scale  by  a  thread 
into  a  vessel  of  water  until  it  is  entirely  submerged.  Does  the 
block  appear  to  weigh  as  much  now  as  when  out  of  water? 

Compare  the  difference  between  the  weight  of  the  block  in  air 
and  its  apparent  weight  in  water,  with  the  weight  of  the  water 
which  the  block  displaced  in  the  preceding  experiment.  One  cubic 
centimeter  of  water  weighs  a  gram. 

From  this  experiment  we  learn  that  a  body  appears  to 
lose  weight  when  it  is  submerged  in  water  and  the  amount 
of  weight  it  loses  is  exactly  equal  to  the  weight  of  the  vol- 
ume of  water  it  displaces.  If  a  cubic  centimeter  of  lead  is 
weighed  in  water  it  will  be  found  to  weigh  one  gram  less  than 
in  air.  In  other  words  the  lead  is  pushed  upward,  or  buoyed 
up,  by  a  force  exactly  equal  to  the  weight 
of  a  like  volume  of  water. 

Experiment  70.  —  If  convenient  use  an  "  over- 
flow can."  If  not  punch  a  hole  near  the  top  of 
a  large  tin  can.  (Drive  the  punch  from  the 
inside  so  that  the  flange  will  be  on  the  out- 
side.) Smear  a  little  vaseline  around  the  inside 
and  the"  outside  of  the  hole  so  that  water  will 
not  cling  to  the  tin.  Place  the  can  on  a  box  on 
the  table  and  fill  with  water  until  the  water 
begins  to  run  out  of  the  hole.  (Figure  77.)  Accurately  weigh  a 
block  similar  to  the  block  used  in  Experiment  68,  but  containing 
no  lead.  Weigh  also  a  dry  beaker.  Place  the  beaker  so  that  it 
will  cateh  all  the  water  overflowing  from  the  hole  in  the  tin  can. 
Place  the  block  in  the  can.  As  soon  as  water  has  ceased  to  run 


FIGURE  77 


150       THE  WATERS  OF  THE  EARTH 

into  the  beaker,  weigh  the  beaker  with  the  water  in  it.  Subtract  the 
weight  of  the  dry  beaker  from  the  weight  of  the  beaker  containing 
water,  and  you  will  have  the  weight  of  the  water  displaced  by  the 
block  of  wood.  Compare  this  weight  with  the  weight  of  the  block. 
Mark  on  the  block  the  depth  to  which  it  sinks.  About  how 
much  of  the  block  was  submerged  ? 

A  body  floating  in  water  displaces  its  own  weight  of  water. 
Thus  if  a  body  is  half  as  dense  as  water,  it  will  sink  half 


AN  AMERICAN  SUBMARINE 

its  volume ;  if  one  third  as  dense,  it  will  sink  one  third  its 
volume.  Representing  the  density  of  water  by  1,  what  deci- 
mal fraction  would  represent  the  approximate  density  of  the 
wood  in  the  experiment  ?  The  density  of  any  substance  as 
compared  with  the  density  of  water  is  known  as  the  specific 
density  of  the  substance.  A  solid  piece  of  iron  is  much 
denser  than  water  and  when  submerged  displaces  much  less 
than  its  own  weight  of  water.  It  therefore  sinks.  But  an 
iron  dish  will  float  because  its  volume  is  so  great  that  it 
displaces  a  weight  of  water  equal  to  its  own  weight.  If  a 
hole  is  made  in  the  dish  and  water  is  allowed  to  enter  the 


ANIMAL  LIFE   IN  WATER  151 

hollow  space,  the  dish  begins  to  sink.  The  depth  to  which 
it  sinks  may  be  regulated  by  the  amount  of  water  admitted. 
Submarines  are  boats  so  constructed  as,  to  be  water-tight 
even  when  submerged.  Special  compartments  are  provided 
to  which  water  can  be  admitted  and  from  which  it  can  be 
driven  out.  When  the  commander  of  a  submarine  wishes  to 
submerge  his  vessel,  he  gives  the  order  to  admit  sufficient 
water  to  the  compartments  to  make  the  submarine  heavier 


SUBMARINE  SUBMERGING 

than  an  equal  volume  of  water.  It  therefore  sinks.  In  order 
to  make  the  submarine  rise,  the  operators  must  force  water 
out  of  the  tanks  until  the  submarine  displaces  a  weight  of 
water  greater  than  its  own  weight.  It  will  then  rise  and 
float  partly  submerged.  If  just  enough  water  is  admitted  to 
the  tanks  to  make  the  weight  of  the  submarine  equal  to  the 
weight  of  the  water  displaced,  the  submarine  can  be  made  to 
float  at  varying  depths. 

Animal  Life  in  Water.  —  From  previous  experiments  we 


152 


THE   WATERS   OF   THE    EARTH 


have  learned  some  of  the  chief  physical  properties  of  water, 
and  so  perhaps  we  can  understand  the  different  effects  that 
water  has  had  upon  the  development  and  activities  of 
living  things.  Some  water  animals  move  about  easily  to 
get  their  food,  but  others  have  it  brought  to  them  in  solution 
and  so  obtain  it  without  muscular  effort.  The  air  that  they 
breathe  is  in  solution  and  they  cannot  as  easily  obtain  a 

large  quantity  of  it  as 

can  the  land  animals. 
Since  the  energy  of  all 
animals  depends  upon 
the  amount  of  oxygen 
they  use  in  their  bodies, 
the  water  animals  are 
generally  less  energetic 
than  the  land  animals. 
Since  they  also  have 
such  an  easy  time  in 
moving  or  floating  about 

to  get  the  things  they  need  they  have  not  developed  as 
high  organisms  as  the  land  animals. 

Ocean  Waters.  —  The  oceans  which  cover  almost  three 
fourths  of  the  earth's  surface  are  the  inexhaustible  reser- 
voirs from  which  come,  directly  or  indirectly,  the  waters  of 
rivers  and  lakes,  of  wells  and  springs,  and  the  moisture  of 
atmosphere  and  soil. 

Experiment  71.  —  If  ocean  water  can  be  obtained,  boil  down 
about  a  pint  of  it  in  an  open  dish.  Taste  the  residue.  What  is 
the  principal  constituent  of  this  residue  ? 

There  is  probably  no  water  on  the  surface  of  the  earth 
which  is  absolutely  pure.  All  ordinary  water  has  come  in 
contact  with  some  substances  which  it  could  dissolve. 


CORALS 

Fixed  animals  whose  food  is  brought  to 
them  in  solution  by  the  ocean  currents. 


OCEAN  WATERS 


153 


When  the  river  waters  run  into  the  sea,  they  carry  with  tjaem 
whatever  they  have  dissolved  from  the  land.  When  the 
water  of  the  sea  evaporates  and  is  borne  away,  to  fall  upon 
the  land  again,  the  dissolved 
material  is  left  behind  in 
the  ocean. 

Thus  the  sea  has  for  all 
time  been  receiving  soluble 
contributions  from  the  land. 
It  is  easy  to  prove  that  it 
contains  salt,  for  we  can 
taste  it.  It  must  contain 
lime,  since  coral  and  shell 
animals  of  the  sea  depend 
upon  it  for  the  hard  parts 
of  their  bodies.  There  must 

be  organic  food  material  in  it,  or  else  fixed  animals  like 
corals  could  not  get  their  food.  It  contains  air,  for  with- 
out air  fishes  could  not  breathe.  These  are  the  principal 
substances  which  we  need  consider  in  the  study  of  ocean 
water,  but  the  chemist  can  find  many  other  substances 
dissolved  in  it.  There  is  so  much  dissolved 
material  of  different  kinds  in  it  that  the  density 
of  the  solution  is  sufficient  to  keep  ocean  water 
from  freezing  until  it  reaches  28°  F.,  instead  of 
32°  F.,  the  temperature  at  which  fresh  water 
(  11  I  freezes. 


small  stream  from  the  tube  stirs  up 
the  tank-water  and  causes  it  to 
absorb  air. 


if! 


Experiment  72.  —  Place  in  a  deep  dish  of  fresh 
FIGURE  78    water  a  density    hydrometer   (Figure    78),   or    stick 
loaded  with  lead  at  one  end  so  that  it  will  float  up- 
right.    Mark  with  a  rubber  band  the  depth  to  which  the  hydrom- 
eter   sinks  in  the  water.      Now   place    the    hydrometer  in  sea 


154 


THE    WATERS   OF   THE    EARTH 


water  and  mark  the  depth  to  which  it  sinks.  If  sea  water  cannot 
be  obtained,  dissolve  in  a  pint  of  fresh  water  about  15  g.,  or  half 
an  ounce,  of  salt.  This  will  give  the  water  about  the  same  amount 
of  dissolved  solid  material  as  sea  water  has.  About  how  much 
more  of  its  length  does  the  hydrometer  sink  in  fresh  water  than 
in  sea  water?  Will  a  piece  of  ice  project  more  out  of  salt  water 
than  it  would  out  of  fresh  water? 

On  account  qf  the  materials  dissolved,  sea  water  weighs 
more  than  fresh  water,  or  has  a  greater  specific  density. 
Floating  bodies  therefore  have  less  of  their  volumes  sub- 
merged in  sea  water  than  in  fresh  water.  A  cubic  foot  of 
sea  water  weighs  over  64.25  pounds,  whereas  a  cubic  foot 
of  fresh  water  weighs  only  about  62.5  pounds.  The  specific 
density  of  sea  water  is  about  1.03. 

Ocean  Depths.  —  The  greatest  depth  thus  far  found  in 
the  ocean  is  over  six  miles.  .  This  was  found  in  the  Pacific 

Ocean  near  the  Philippine 
Islands.  The  greatest 
depth  in  the  Atlantic 
Ocean  thus  far  discov- 
ered is  a  little  over  five 
miles  at  a  point  north 
of  Porto  Rico.  The 
average  depth  of  the  sea 
is  probably  about  two 
and  one  half  miles. 


MOUNT  EVEREST 


As  it  would  appear  if  placed  in  the 
deepest  part  of  the  sea. 


Although  the  pressure 
at    the    bottom    of    the 

ocean  must  be  tremendous,  yet  so  incompressible  is  water 
that  a  cubic  foot  of  it  weighs  but  little  more  at  the  bottom 
of  the  sea  than  it  does  at  the  top.  Thus  a  body  which 
readily  sinks  will  in  time  reach  the  bottom,  no  matter  what 


CONDITIONS  OF  THE   OCEAN  FLOOR  155 

the  depth  may  be.  At  a  depth  of  two  miles  the  pressure 
is  over  300  times  as  much  as  at  the  surface  of  the  water; 
and  here,  as  we  have  already  found,  it  is  about  15  pounds 
to  the  square  inch. 

If  a  bag  of  air  which  had  a  volume  of  300  cubic  inches 
at  the  surface  were  sunk  in  the  ocean  to  a  depth  of  two 
miles,  it  would  have  a 
volume  of  less  than  a 
cubic  inch,  and  the  pres- 
sure upon  it  would  be 
several  tons.  It  thus 
happens  that  deep  sea 
fishes  when  brought  to 
the  surface  have  the  air 
in  their  swimming  blad- 
ders so  expanded  that  the 
bladders  are  often  blown 
out  of  their  mouths. 

Conditions  of  the  Ocean 
Floor.  —  The  ocean  floor 
is  a  vast,  monotonous, 
nearly  level  expanse  whose  CRINOID 

dreary,  slimy,  and   almost        A  «»  animal  once  abundant  but  now 

found  only  in  deep  oceans. 

lifeless  surface  is  enveloped 

in  never-ending  night  and  is  pressed  upon  by  a  vast  weight 
of  almost  stagnant  frigid  water.  Here  and  there  volcanoes 
rise  upon  it  with  gradually  sloping,  featureless  cones,  and 
sometimes  a  broad,  wavelike  swell  reaches  within  a  mile  or 
so  of  the  surface.  Such  a  swell  extends  along  the  center  of 
the  Atlantic  Ocean  through  Ascension  Island  and  the 
Azores. 


156        THE  WATERS  OF  THE  EARTH 

There  are  no  hills  and  vales,  no  mountain  ranges  having 
sharp  peaks  and  deep  valleys.  Gradually  rising  ridges 
and  volcanoes,  sometimes  topped  with  coral  islands,  alone 
vary  the  monotony.  It  is  the  nether  world  of  gloom  and 
unaltering  sameness.  Here  the  derelicts  of  ages  past,  after 
their  fierce  buffeting  with  wind  and  wave,  have  found  a  quiet,  ' 
changeless  haven  where  they  may  lie  undisturbed  until 
absorbed  into  the  substance  of  the  all-enfolding  water. 

The  Carpet  of  the  Ocean  Floor.  —  Near  the  shore,  the 
floor  of  the  ocean  is  covered  with  sand  and  mud  derived 
from  the  waste  of  the  land.  In  the  deeper  sea  the  cover- 
ing is  a  fine-textured  material  of  animal  origin  called  ooze. 
It  is  composed  of  the  shells  of  minute  animals  that  live 
near  the  surface. 

At  a  depth  of  about  3000  fathoms  (18,000  feet)  these 
shells  disappear  and  a  reddish  clay  appears.  This  clay  is 
believed  to  be  due  to  meteoric  and  volcanic  dust  and  to 
the  insoluble  parts  that  remain  after  the  calcareous  (lime- 
like)  material  of  the  minute  shells  has  been  dissolved  in 
sinking  through  the  deep  water.  No  layers  of  this  kind 
have  ever  been  found  on  the  land,  and  this  is  one  of  the 
reasons  for  believing  that  the  depths  of  the  sea  have  never 
been  elevated  into  dry  land,  but  that  what  is  now  deep 
ocean  has  throughout  all  time  been  deep  ocean. 

Temperature  of  Ocean  Waters.  —  Sea  water  continues 
to  contract  as  it  cools  until  it  is  of  about  the  freezing  tem- 
perature of  fresh  water.  Hence  cold  water  near  the  poles 
gradually  sinks  and  creeps  under  the  wrarmer  water  of 
lower  latitudes,  maintaining  a  temperature  of  32°  to  35° 
on  the  bottom,  even  at  the  equator.  This  steady  creep  of 
cooled  surface  water  along  the  bottom  supplies  the  animals 


WAVES  157 

of  the  deep  ocean  floor  with  the  air  which  they  must  have. 
Without  it  the  water  at  great  depths  would  have  its  air 
exhausted  and  all  life  would  be  destroyed. 

At  the  surface  of  the  ocean  the  temperature  of  the  water 
varies  in  a  general  way  with  the  latitude;  it  is  over  80° 
at  the  tropics  and  about  the  freezing  point  at  the  poles. 
Near  the  poles  and  near  the  equator  there  is  very  little 
variation  in  the  temperature  of  the  surface  water  during 
the  year,  but  in  the  intermediate  latitudes  the  annual 
variation  is  considerable.  Below  the  surface  the  effect 
of  solar  heat  rapidly  diminishes  and  at  a  depth  of  300  ft. 
it  is  probable  that  the  annual  variation  in  temperature  is 
nowhere  more  than  2°  F.  Below  600  ft.  there  is  probably 
no  annual  change  in  temperature. 

Waves.  —  Experiment  73.  —  Take  a  long,  flexible  rubber  band 
or  tube  and  having  fastened  one  end,  stretch  it  somewhat.  Now 
strike  down  on  it  near  one  end  with  a  small  stick.  A  wavelike 
motion  will  be  seen  to  travel  from  end  to  end  of  the  band.  It  is 
evident  that  the  particles  of  rubber  do  not  enter  into  the  lateral 
movement,  but  that  they  simply  move  up  and  down,  whereas  the 
,wave  movement  proceeds  along  the  band.  A  piece  of  paper  folded 
and  placed  lightly  upon  the  band  will  move  up  and  down  but  not 
along  the  band.  Thus,  wave  motion  does  not  necessitate  lateral 
movement  of  the  particles  taking  part  in  the  wave. 

When  the  wind  blows  over  water,  it  throws  the  surface 
into  motion  and  produces  waves.  The  highest  part  of  the 
wave  is  called  the  crest  and  the  lowest  part  the  trough. 
Trough  and  crest  move  along  rapidly  over  the  surface  of 
the  water.  The  particles  of  the  water  themselves,  how- 
ever, move  somewhat  like  those  in  the  rubber  band.  That 
the  water  itself  does  not  move  with  the  wave  can  be  seen 
when  a  floating  bottle  is  observed.  It  moves  up  and  down 


158 


THE   WATERS   OF   THE    EARTH 


but  does  not  move  forward.  If  the  water  moved  along 
with  the  waves,  it  would  be  next  to  impossible  to  propel  a 
boat  against  the  direction  of  the  wave  movement. 

That  it  is  possible  to  generate  wave  movement  without 
the  particles  themselves  moving  along  with  the  wave  is 
seen  when  a  field  of  grain  is  bending  before  a  gentle  wind. 
The  troughs  and  crests  move  one  after  the  other  across  the 


field  but  the  heads  of  grain  simply  vibrate  back  and  forth. 
The  crest  of  a  water  wave,  however,  is  often  blown  forward 
by  the  wind  and  thus  a  drift  in  the  direction  of  the  wind  is 
established  at  the  surface. 

When  great  waves  are  raised  by  the  wind  at  sea,  there 
is  danger  that  the  mighty  crests  may  be  blown  forward 
and  engulf  a  ship.  To  calm  the  waves  ships  sometimes 
pour  "oil  on  the  troubled  waters."  The  oil  spreads  out 
in  a  thin  film  over  the  water  and  forms  a  "  slick  "  which 


WAVES  AS  DESTROYERS  AND  BUILDERS        159 

prevents  the  wind  from  getting  sufficient  hold  upon  the 
water  to  topple  over  the  crests,  and  thus  the  danger  of  being 
swamped  is  averted.  It  has  been  found  that  oil  will  spread 
out  even  in  the  direction  of  the  severest  wind. 

Although  sometimes  waves  are  spoken  of  as  "  mountain 
high,"  it  rarely  happens  that  the  height  from  trough  to 
crest  is  over  50  ft.  The  movement  of  the  waves  stirs  up 
the  water  and  enables  it  more  freely  to  absorb  the  air  which 
is  so  necessary  for  the  existence  of  water  animals. 


FINGAL'S  CAVE 

Waves  as  Destroyers  and  Builders.  —  Wherever  the 
waves  strike  on  an  unprotected  shore,  they  wear  it  away. 
The  rapidity  of  the  cutting  and  the  forms  carved  depend  upon 
the  strength  of  the  waves  and  the  kind  of  shore.  Wherever 
there  is  a  point  of  weakness  along  the  shore,  there  the  waves 
cut  back  more  rapidly.  The  harder  parts  stand  out  sharply 


160 


THE   WATERS  OF  THE   EARTH 


as  points  and  promontories.     In  some  cases  the  waves  cut 

back  so  rapidly  on  lofty  coasts  that  high  cliffs  are  formed. 
If  the  material  of  the  coast  does  not  readily  break  off 

when  undercut  by  the  waves,  a  sea  cave  may  be  formed. 

Such  is  the  well-known  Fingal's  Cave  on  an  island  off  the 

coast  of  Scotland 
where  the  structure 
of  one  of  the  igneous 
rock  layers  allows  the 
waves  to  quarry  it 
comparatively  easily. 
If  a  coast  stays  at 
the  same  elevation 
long  enough,  or  if  its 
material  is  easily 
eroded,  large  areas 
of  what  was  for- 
merly dry  land  may 
be  cut  away  and 
brought  under  the 
sea. 

In  1399  Henry  of 
Lancaster,  afterward 

A  year  after  this  picture  was  taken  a  landslide      Henry    IV    of    Eng- 


A  LAKE  BEACH  FORMED  BY  A  STREAM  AND 
WAVE  ACTION 


caused  a  wave  which  swept  away  the  entire 
beach  and  village. 


land,  returned  from 
his  exile  and  landed 
at  Ravenspur,  an  important  town  in  Yorkshire,  to  begin 
his  fight  for  the  crown.  A  person  disembarking  at  the 
same  place  to-day  would  be  so  far  from  shore  that 
he  would  need  to  be  a  sturdy  swimmer  to  reach  the 
beach.  The  entire  area  of  the  ancient  town  has  been 
cut  away  by  the  waves  and  now  lies  under  the  sea.  This 


WAVES  AS  DESTROYERS  AND  BUILDERS        161 

is  an  example    of   what   has   occurred    in  many  seacoast 
regions. 

Unless  the  material  pillaged  from  the  land  by  the  waves 
falls  into  too  deep  water,  it  is  buffeted  about  by  them  and 
broken  and  worn  into  small  pieces.  These  are  then  borne 
along  by  the  shore  currents  until  they  find  lodgment  in 
some  protected  place  where  they  can  accumulate.  When 
sufficient  material  has  been  accumulated,  the  storm  waves 


A  SAND  SPIT,  FORMED  BY  WAVES  AND  CURRENTS 

and  the  wind  sweep  some  of  it  above  sea  level  and  fringe 
the  water's  edge  with  a  border  of  water- worn  sand  and 
pebbles.  These  accumulations  of  shore  drift  are  called 
beaches. 

Currents  moving  loose  material  with  them  sometimes 
form  it  into  bars  which  tie  islands  to  the  mainland  or  extend 
into  the  sea  free  ends,  forming  what  are  called  spits.  A 
famous  example  of  a  land-tied  island  is  that  of  the  great  Eng- 
lish fortress  at  Gibraltar.  Although  now  a  promontory,  it 


162       THE  WATERS  OF  THE  EARTH 

was  once  an  island  detached  from  the  coast  of  Spain.  Shift- 
ing sand  bars,  especially  if  covered  with  water,  are  exceed- 
ingly dangerous  to  vessels,  and  coasts  where  these  are  abun- 
dant need  especial  protection  by  lighthouses  and  life-saving 
stations.  The  greatest  Mediterranean  port  of  France  during 
the  thirteenth  century,  Aigues-Mortes,  has  been  closed  in 
by  sand  bars  so  that  there  is  no  longer  access  to  the  sea  and 
only  the  relics  of  the  former  great  city  now  exist.  Thus 
have  the  moving  sea-sands  overthrown  the  plans  of  men. 

Ocean  Currents.  —  The  ocean  is  a  region  of  never-ceasing 
motion.  At  considerable  depths  its  motion  is  very  slow, 
but  near  the  surface,  where  the  prevailing  winds  can  affect 
it,  the  movement  is  considerable.  Circulating  around  each 
ocean  there  is  a  continuous  drift  of  surface  water  extending 
to  a  depth  of  from  300  to  600  feet  and  varying  in  rate  from 
a  few  miles  up  to  fifty  or  more  miles  a  day.  In  fact  these 
rotating  currents  are  the  chief  natural  basis  for  the  divi- 
sion of  the  oceanic  area  into  six  oceans,  as  our  geographies 
generally  divide  them. 

These  currents  circulate  in  the  northern  hemisphere  in 
the  direction  in  which  the  hands  of  a  watch  move  and  in 
the  southern  hemisphere  in  the  opposite  direction.  In 
the  centers  of  these  rotating  areas  the  water  is  nearly  motion- 
less and  here  are  often  found  great  masses  of  floating  sea- 
weed filled  with  a  great  variety  of  small  animals.  These 
accumulations  of  seaweed  are  called  sargasso  seas. 

The  temperature  of  winds  blowing  from  the  sea  is  modi- 
fied by  these  currents  and  greatly  affects  the  habitability 
of  the  earth  for  man.  The  editor  of  the  National  Geographic 
Magazine  makes  the  striking  statement  that  "the  Gulf 
Stream  carries  enough  heat  toward  Europe  every  twenty- 


164 


THE   WATERS   OF   THE    EARTH 


four  hours  to  melt  a  mass  of  iron  as  large  as  Mount  Wash- 
ington. Hammerfest  at  71Q  north  is  a  flourishing  seaport, 
but  there  are  no  important  settlements  above  50°  on  the 
western  side  of  the  Atlantic.  Alaska,  the  prevailing  winds 
of  which  are  warmed  by  blowing  over  the  warm  ocean, 
is  a  region  which  promises  much  for  human  habitation, 
while  the  region  on  the  opposite  side  of  the  Pacific  must 
remain  almost  destitute  of  human  inhabitants.  It  should 

be  noted  that  the 
effect  of  the  warm 
ocean  waters  would 
be  slight,  except 
along  the  coast,  were 
it  not  for  the  air 
movements. 


HIGH  TIDE  IN  NOVA  SCOTIJ 


Tides. —  Prob- 
ably the  first  thing 
that  impresses  us 
on  visiting  the  sea- 
shore is  the  regular 
rising  and  falling  of 
the  water  each  day. 
These  movements  of  the  water  are  called  tides.  If  we 
observe  the  tides  for  a  few  days,  we  find  that  there  are  two 
high  and  two  low  tides  each  day.  As  the  tidal  current 
comes  in  from  the  open  ocean  and  the  water  rises,  it  is 
called  flood  tide,  and  as  it  runs  out  or  falls,  ebb  tide.  When 
the  tides  change  from  flood  to  ebb  or  ebb  to  flood,  there  is 
a  brief  period  of  "  slack  water." 

If  we  observe  closely,  we  shall  see  that  the  corresponding 
tides  are  nearly  an  hour  later  each  day  than  they  were 


TIDES 


165 


the  day  before,  and  that  the  time  required  for  the  comple- 
tion of  two  high  and  two  low  tides  is  nearly  25  hours.  Con- 
tinued observation  will  show,  as  Julius  Caesar  stated  many 
centuries  ago,  that  there  is  apparently  a  relation  between 
the  phases  of  the  moon  and  the  height  of  the  tides.  The 
greatest  rise  and  fall  of  the  water  will  be  found  to  occur 
about  the  time  of  full  and  new  moon. 

It  has  been  found  that  the  position  of  the  sun,  as  well  as 
that  of  the  moon, 
affects  the  height  of 
the  tide.  If  the 
earth,  moon,  and 
sun  lie  in  nearly 
the  same  line,  the 
tidal  range  is  great- 
est. This  is  called 
spring  tide.  When 
the  sun  and  moon 
act  at  right  angles 
upon  the  earth,  the 
tidal  range  is  least 
and  this  is  called 


Low  TIDE  A 


E  SAME  PLACE 


neap  tide.  The  tidal 
undulations  have  been  proved  by  astronomers  to  be  due  to 
the  rotation  of  the  earth  and  the  gravitational  attraction  of 
the  sun  and  moon  upon  its  water  envelope.  The  moon  is 
much  more  effective  because  it  is  nearer. 

The  tidal  current  as  it  sweeps  between  islands  often 
forms  eddies  and  whirlpools  which  make  navigation  very 
dangerous.  An  example  of  this  is  found  at  Hell  Gate, 
New  York,  and  at  the  famous  Maelstrom  off  the  coast  of 
Norway.  On  the  other  hand,  in  flat  countries  where  the 


166       THE  WATERS  OF  THE  EARTH 

rivers  are  shallow,  ports  which  could  not  otherwise  be 
reached  are  made  accessible  to  ships  of  considerable  burden 
at  the  time  of  high  tide.  At  these  places  the  time  of  leav- 
ing or  making  port  changes  each  day  with  the  time  of  high 
tide.  A  striking  example  of  this  is  the  port  of  Antwerp. 

The  tidal  currents  are  also  continually  changing  the  water 
in  bays  and  harbors  and  thus  keeping  them  from  becoming 
stagnant  and  foul.  They  also  bring  food  to  many  forms  of 
inshore  life  which  have  but  little  or  no  power  of  movement, 
such  as  clams  and  other  shellfish.  The  ebb  of  the  tide 
exposes  some  of  these  and  gives  man  a  chance  to  acquire 
them  readily  for  food. 

Man  and  the  Ocean.  —  At  first  thought  it  would  seem 
better  for  the  life  of  the  world  if  the  proportion  of  land  and 
water  were  reversed.  Yet  when  we  consider  that  almost 
barren  wastes  constitute  many  continental  interiors  and  that 
plenty  of  rainfall  is  necessary  to  make  land  habitable, 
the  utility  of  the  great  water  surfaces  becomes  apparent. 
From  the  evaporation  of  the  ocean  surface  comes  nearly 
all  the  water  which  supplies  man,  land  animals,  and  plants. 

It  is  not  only  true  that  all  streams  eventually  run  to  the 
sea  but  it  is  also  true  that  all  their  water  comes  from  the 
sea.  Other  things  being  equal,  the  smaller  the  surface  for 
evaporation  the  less  the  water  supplied  to  the  land.  Be- 
sides supplying  the  land  with  water,  the  ocean  has  a  great 
effect  on  its  climate. 

The  animals  of  the  sea  also  furnish  food  for  thousands. 
The  value  of  the  world's  fishery  products  is  nearly  one  half 
billion  dollars  a  year.  A  large  part  of  the  earth's  population 
is  now,  and  always  has  been,  located  not  far  from  the  shore 
of  the  ocean. 


SUMMARY  167 

In  early  times  before  the  advent  of  railways  almost  all 
commerce  was  carried  on  over  the  sea.  Even  now  this  is 
the  cheaper  way  of  transportation.  Modern  methods  of 
conveyance  have  enabled  man  to  live  with  comfort  at  a 
considerable  distance  from  the  ocean,  but  the  dry  interiors 
of  continents  still  remain  sparsely  inhabited.  All  com- 
mercial nations  must  have  an  outlet  to  the  sea  and  to  ob- 
tain it  much  blood  and  treasure  have  often  been  spent. 

SUMMARY 

The  earth  has  been  called  a  water  engine  since  water  has 
played  such  an  important  part  in  its  history.  Pure  water 
is  a  colorless,  odorless,  tasteless  liquid,  composed  of  two 
gases,  hydrogen  and  oxygen.  Water  may  evaporate  at 
any  temperature,  but  evaporation  goes  on  most  rapidly  at 
the  boiling  point.  As  water  above  4°  C.  increases  in 
temperature,  it  increases  in  volume.  When  water  changes 
from  a  liquid  to  a  gas,  its  volume  increases  more  than  1700 
times.  Water  in  cooling  grows  denser  until  it  reaches  about 
4°  C.  It  then  begins  to  expand  and  continues  to  do  so  until 
it  freezes  at  0°  C.  When  it  freezes  it  exerts  a  pressure  of 
more  than  100  tons  to  the  square  foot.  The  entire  mass  of 
a  body  of  water  must  reach  a  temperature  of  about  4°  C. 
before  it  begins  to  freeze  at  the  surface. 

Water  is  the  greatest  of  all  solvents  but  it  does  not  dissolve 
every  substance.  The  higher  the  temperature  of  water,  the 
less  air  but  the  more  solid  matter  it  will  hold  in  solution.  A 
mixture  of  ice,  salt  and  water  is  called  a  freezing  mixture  be- 
cause the  solution  attains  a  temperature  lower  than  that  of 
melting  ice.  All  solutions  freeze  at  a  lower  temperature  than 
that  at  which  pure  water  freezes.  Water  may  also  hold  sub- 
stances in  suspension.  The  greater  the  movement  of  water 


168        THE  WATERS  OF  THE  EARTH 

the  more  it  will  hold  suspended  in  it.  Oils  and  fats,  which  do 
not  dissolve  in  water,  may  be  suspended  in  water  by  emulsion. 

Water,  like  air,  exerts  pressure,  the  amount  of  which  de- 
pends on  the  depth  of  the  water.  The  pressure  at  any  given 
depth  is  equal  in  all  directions.  Water  also  transmits 
pressure  equally  in  all  directions. 

A  submerged  body  displaces  a  volume  of  water  equal  to 
its  own  volume,  and  loses  weight  exactly  equal  to  the  weight 
of  the  water  displaced.  If  a  body  weighs  less  than  an  equal 
volume  of  water  it  floats ;  if  more,  it  sinks. 

Animals  that  live  in  water  obtain  the  oxygen  they  need 
from  air  in  solution.  Since  an  animal's  energy  depends 
largely  on  the  amount  of  oxygen  it  consumes,  water  animals 
are  generally  less  energetic  than  land  animals. 

The  oceans  are  the  earth's  water  reservoirs.  The  seas  have 
for  all  time  been  receiving  soluble  contributions  from  the  land. 
When  water  evaporates,  the  dissolved  substances  are  left 
behind.  Thus  sea  water  is  denser  than  fresh  water  and 
freezes  at  a  lower  temperature.  The  greatest  depth  thus 
far  found  in  the  ocean  is  more  than  six  miles.  At  the  depth 
of  two  miles,  the  pressure  is  more  than  300  times  as  much 
as  at  the  surface.  The  ocean  floor  is  an  almost  level  expanse 
with  only  occasional  volcanoes  or  gradually  sloping  swells. 
Near  the  shore  mud  and  sand  washed  from  the  land  cover 
the  ocean  floor.  In  deeper  water  the  ocean  floor  is  covered 
with  ooze,  and  below  18,000  feet  with  a  peculiar  reddish 
clay,  not  found  elsewhere.  At  the  surface,  the  temperature 
of  ocean  waters  varies  in  general  with  the  latitude.  Below 
the  surface,  the  effect  of  solar  heat  diminishes  rapidly. 
Below  600  feet  there  is  probably  no  annual  change  in  tem- 
perature, and  at  the  bottom  a  steady  temperature  of  32° 
to  35°  F.  is  maintained. 


QUESTIONS  169 

Waves  are  caused  by  up  and  down,  not  by  lateral,  move- 
ment of  the  water  affected.  The  power  of  waves  and  tides 
to  cause  erosion  results  in  their  acting  as  destroyers  of 
unprotected  shores.  The  solid  matter  eroded  and  carried  in 
suspension  is  often  deposited  at  quieter  places  along  shore. 
Thus  waves  and  tides  may  also  act  as  builders.  Ocean 
currents  are  drifts  of  surface  water,  some  of  which,  due  to 
the  winds  blowing  over  them,  have  very  important  effects 
on  the  climate  of  adjoining  lands.  Tides  are  movements  of 
the  water  envelope  of  the  earth  caused  by  the  rotation  of 
the  earth  and  the  gravitational  attraction  of  the  sun  and  the 
moon  —  chiefly  the  latter.  Oceans  furnish  the  water  which 
supports  land  life,  food  for  thousands  of  people,  and  path- 
ways of  commerce  for  all  nations. 

QUESTIONS 

What  is  the  composition  and  what  are  the  most  striking  charac- 
teristics of  water? 

Why  does  a  freezing  mixture  freeze  substances  placed  in  it  and 
yet  itself  remain  unfrozen? 

What  is  the  difference  between  an  emulsion  and  a  solution? 

Why  is  soap  used  in  cleaning? 

Explain  the  principle  of  the  hydraulic  press. 

How  could  a  piece  of  lead  be  made  to  float  in  water?      Why? 

Mention  some  ways  in  which  ocean  water  differs  from  distilled 
water. 

Waves  and  currents  are  -both  primarily  due  to  winds.  How 
do  they  differ  in  action  and  effect? 

What  are  tides  and  their  cause  ? 

Of  what  advantage  is  the  ocean  to  man? 


CHAPTER  VII 

THE  WORK   OP  RUNNING  WATER 

The  Sphere  of  Activity  of  Rain.  —  When  rain  falls  upon 
the  ground,  it  may  do  one  of  three  things.  It  may  evapo- 
rate immediately  from  the  surface  and  return  to  the  air ; 
or  it  may  run  rapidly  off  the  surface  and  quickly  join 
the  streams  and  rivers  which  bear  it  to  its  final  goal,  the 
sea;  or  it  may  sink  into  the  ground.  In  this  last  case 
part  of  it  returns  gradually  through  capillary  action  to 
the  surface,  where  it  is  again  evaporated ;  part  finds  its 
way  into  springs;  and  part  sinks  deep  into  the  soil  and 
rock. 

Experiment  74.  —  (Teacher's  Experiment.)  —  Attach  one  end  of  a 
rubber  tube  to  a  faucet  in  a  sink.  In  the  other  end  of  the  rubber 

tube  insert  a  glass  tube 
drawn  out  to  a  point,  so 
that  when  the  faucet  is 
opened  the  water  will  issue 
from  the  glass  tube  in  a  fine 
FIGURE  79  stream.  Arrange  to  play 

this  stream  into  the  concave 

surface  of  a  spoon  so  that  the  reflected  and  widened  spray  will  fall 
over  about  a  square  foot  of  surface.     (Figure  79.) 

Take  a  long,  shallow,  flat-bottomed  pan  and  punch  a  row  of  holes 
in  one  end  of  it,  a  little  above  the  bottom.  At  the  other  end,  and 
covering  about  two  thirds  of  the  bottom  of  the  dish,  arrange  several 
thin,  irregular  layers  of  fine  sand,  salt,  fine  clay,  coal  dust,  or 
other  fine  materials.  Tilt  the  pan  slightly  so  that  the  fine  materials 
170 


LAKES  171 

may  occupy  the  upper  two  thirds  of  a  gentle  slope  and  the  bare 
surface  of  the  pan  with  the  drainage  holes,  the  lower  one  third. 

Allow  the  spray  fromi 
the  spoon  to  play  over  the 
layers  in  the  dish  for  some 
time.  Tiny  rivulets  will 
grow  in  the  layered  sur- 
face, gradually  deepening 
and  extending  their  valleys,  FIGURE  80 

and  more  and  more  thor- 
oughly dissecting  the  surface.     Deltas  will  be  formed  in  the  still 
water  in  the  lower  part  of  the  pan,  and  many  of  the  erosion 
phenomena  of  a  stratified,   slightly  elevated  region  will  appear. 
(Figure  80.) 

Run-off.  —  The  rain  that  falls  upon  the  land  and  neither 
evaporates  nor  sinks  into  the  surface  runs  off  as  fast  as  it 
can  toward  the  sea.  It  is  joined  sooner  or  later  by  the 
water  from  the  springs  and  by  the  rest  of  the  underground 
drainage.  Sometimes  the  journey  is  long  and  there  are  many 
stops  and  delays  in  lakes  and  pools;  sometimes  the  course 
is  quite  direct  and  quickly  traveled.  The  run-off  most 
profoundly  affects  the  earth's  surface.  Gullies  and  valleys 
are  cut,  depressions  are  filled ;  in  fact,  running  water  is  the 
chief  tool  which  has  carved  the  features  of  the  earth.  It  has 
had  a  long  time  to  act  and  it  has  kept  unremittingly  busy, 
so  that  the  results  of  its  action  appear  now  in  our  varied 
landscape. 

Lakes.  —  The  water  which  runs  off  the  surface  first  fills 
the  depressions.  As  soon  as  these  are  filled,  it  runs  over  the 
lowest  part  of  their  rims  and  starts  again  on  its  course  to 
the  greatest  of  all  depressions,  the  sea.  If  depressions  of 
considerable  size  become  filled  with  water,  we  call  them 
fakes. 


172  THE   WORK   OF   RUNNING  WATER 

The  streams  that  flow  into  lakes  are  continually  bring- 
ing down  the  sand  and  mud  they  have  gathered  in  their 
course,  and  are  thus  filling  up  the  lakes. 

The  outlet  to  a  lake  tends  to  wear  away  its  bed,  but  it 
does  this  slowly,  as  it  has  little  sediment  with  which  to  scour. 
Thus  lakes  are  being  constantly  filled  and  drained,  and  so 
are  comparatively  short-lived  features  of  the  earth. 

Lakes  are  very  important  features  to  man.  They  filter 
river  water  so  that  rivers  emerging  from  lakes  are  clear. 
Where  the  Rhone  enters  Lake  Geneva,  it  is  turbid  and  full 
of  silt,  but  when  it  emerges,  it  is  clear  and  without  sedi- 
ment. Lakes  also  act  as  reservoirs  for  the  water  that  pours 
into  them  at  the  time  of  freshets.  Rivers  emerging  from 
lakes  of  considerable  size  vary  little  in  the  height  of  their 
water  at  different  seasons  of  the  year.  They  are  without 
floods.  The  St.  Lawrence  illustrates  this.  On  the  other 
hand  the  Ohio,  with  its  frequent  and  terribly  destructive 
floods,  shows  the  effect  of  unrestrained  run-off. 

In  some  regions  the  rainfall  is  so  small  that  the  depres- 
sions never  fill  up  sufficiently  to  overflow  their  rims.  The 
water  is  evaporated  from  the  surface  as  fast  as  it  runs 
into  the  lake.  Thus  all  the  salt  and  other  soluble  sub- 
stances which  have  been  extracted  from  the  land  and  brought 
into  the  lake  by  the  rivers  remain  there,  since  only  pure 
water  is  evaporated.  In  this  way  lakes  without  outlet 
become  salt.  Great  Salt  Lake  in  Utah  is  an  example  of 
this.  Some  salt  lakes,  like  the  Caspian  Sea,  were  probably 
once  a  part  of  the  ocean,  so  that  they  have  always  been 
salt. 

As  time  goes  on,  more  salt  is  brought  to  these  lakes  with- 
out outlets,  and  they  become  more  and  more  salty.  Great 
Salt  Lake  has  something  like  14  or  15  per  cent  of  solid 


LAKES 


173 


material  in  its  water,  the  Caspian  Sea  about  13  per  cent, 
and  the  Dead  Sea  about  25  per  cent.  An  effort  to  swim 
in  these  waters  gives  one  an  exceedingly  queer  sensation. 
The  buoyancy  is  so  great  that  a  large  part  of  the  body  is 
out  of  water,  and  one  finds  oneself  bobbing  around  like  a 
cork.  When  boats  pass  from  the  fresh  water  of  the  Volga 


MINING  SALT  IN  THE  DRIED  UP  SALTON  LAKE,  CALIFORNIA 

River  to  the  salt  water  of  the  Caspian  Sea,  their  hulls  grad- 
ually rise  perceptibly  higher. 

Where  bodies  of  water  like  these  have  dried  up,  their  old 
beds  are  exposed  as  almost  level  plains.  These  become 
exceedingly  fertile  under  irrigation  as  soon  as  the  salts  are 
dissolved  and  drained  out  of  the  soil.  Fine  examples  of  this 
are  the  fruitful  plains  near  Salt  Lake  City  and  in  Imperial 
Valley,  California. 


174  THE   WORK   OF   RUNNING   WATER 

Depressions  that  are  very  shallow  and  are  largely  filled 
with  vegetable  growths  are  called  swamps. 

The  Power  of  Running  Water.  —  Running  water  has  the 
power  of  carrying  solid  materials.  If  it  is  moving  slowly, 
this  power  is  not  great;  if  moving  swiftly  and  in  great 
volume,  it  is  tremendous.  The  carrying  power  of  a  stream 


LAKE  DRTJMMOND 

A  lake  in  Dismal  Swamp,  Virginia,  which  is  being  filled  by  vegetable 
growth. 

increases  very  rapidly  if  its  velocity  is  increased.  A  stream 
having  its  velocity  doubled  will  carry  several  times  as 
much  material  as  before.  Thus  it  happens  that  water 
running  over  a  surface  sweeps  loose  material  with  it,  the 
amount  varying  with  the  rapidity  and  volume  of  the  flow- 
ing water. 

As  this  loose  material  sweeps  over  solid  surfaces,  it  cuts 
them  down.     Thus  flowing  water  is  continually  wearing 


DIVIDES  175 

down  and  sweeping  away  the  surface  over  which  it  moves. 
This  sort  of  work  is  called  water  erosion. 

When  running  water  is  concentrated  into  a  stream,  the 
work  of  erosion  is  also  concentrated  and  the  wearing  down 
of  the  stream  bed  becomes  comparatively  rapid.  This 
cutting  down  goes  on  irregularly,  being  greatest  at  time  of 
flood  and  least  when  the  flow  is  slight. 


GULLIES  BEING  CUT  BY  RUNNING  WATER 

Divides.  —  If  we  carefully  observe  the  drainage  of  a 
region,  we,  find  that  the  areas  from  which  different  streams 
gather  their  water  are  usually  so  distinctly  separated  from 
one  another  that  a  line  could  be  drawn  so  that  wherever 
water  falls  the  rivulets  on  one  side  would  flow  into  one 
stream  and  on  the  other  side  into  another.  Such  a  line  of 
the  highest  land  between  the  drainage  areas  of  neighboring 
streams  is  called  a  divide.  The  line  may  be  very  distinctly 
marked,  as  on  mountain  ridges,  or  it  may  be  difficult  to 
determine,  as  in  a  flat  country,  but  if  the  drainage  is  well 
established,  it  will  be  apparent. 


176  THE   WORK   OF   RUNNING   WATER 

If  the  drainage  is  not  well  established,  areas  may  be 
found  which  at  one  time  drain  in  one  direction  and  at  an- 
other time  in  another. 

Thousands  of  years  ago,  during  the  Glacial  Period, 
Lake  Michigan  drained  into  the  Mississippi  system.  In 
recent  geological  times  it  has  drained  into  the  St.  Lawrence 
system.  Chicago,  by  dredging  a  drainage  canal  along  an 


DIVIDES  BETWEEN  STREAMS 

The  ridge  in  the  center  of  the  picture  separates  two  streams  flowing  in 
opposite  directions. 

ancient  outlet,  has  restored  part  of  the  drainage  of  the  lake 
to  the  Mississippi  system. 

Divides  are  irregular  in  their  height,  so  that  roads  and 
railways  in  passing  from  one  drainage  basin  to  another 
usually  seek  out  the  lowest  part  of  the  divide.  In  mountain 
regions  these  low  places  are  called  passes. 

River  Development.  —  The  rain  which  falls  upon  a 
flat  country  runs  off  very  slowly,  a  large  part  of  it  soaking 


RIVER  DEVELOPMENT 


177 


Into  the  ground.  Pools  and  lakes  are  formed  in  the  in- 
closed basins,  and  sluggish  streams  with  irregular  little 
crooks,  which  show  that  the  streams  have  hardly  decided 
where  they  want  to  go,  wander  in  the  slight  depressions 


NIAGARA  FALLS 

down  the  gentle  slopes  and  unite  with  other  streams 
here  and  there  until  a  river  of  ever  increasing  size  is 
formed. 

In  some  places  the  streams  flow  through  lakes  where 
they  deposit  their  sediment,  thus  filling  the  lake  basins. 
Here  and  there  they  pass  over  hard  layers  of  rock  which 


178  THE   WORK   OF   RUNNING   WATER 

hold  them  up  in  falls  and  rapids.  These  they  at  once 
begin  to  smooth  down.  Rivers  of  this  kind  may  well  be 
called  young,  as  their  life  work  is  just  beginning.  The 
Red  River  of  the  North,  with  its  shallow,  narrow  valley 
and  tortuous  course,  and  the  Niagara  River,  with  its  lakes 
and  falls,  are  examples  of  young  rivers. 


STREAM  WORKING  BACK  INTO  AN  UND'ISSECTED  AREA 

Where  the  slope  of  the  newly  exposed  surface  is  consid- 
erablcj  the  streams  flow  much  more  rapidly  and  develop 
their  courses  more  quickly.  The  small  irregularities  are 
sooner  straightened  and  the  trough  deepened,  thus  form- 
ing side  slopes  down  which  run  little  rivulets  which  in 
time  form  side  streams.  The  heads  of  these,  like  the  heads 
of  the  larger  streams,  are  constantly  working  back  into  the 
undissected  area.  Gradually  the  side  streams  develop  side 


RIVER  DEVELOPMENT  179 

streams  of  their  own,  and  almost  the  whole  surface  is  covered 
with  a  network  of  streams. 

As  the  work  of  erosion  goes  on  and  the  streams  deepen 
their  valleys,  only  a  few  imperfectly  drained  remnants  of 
the  former  flat  surface  are  left  here  and  there.  These  lie 


YELLOWSTONE  RIVER 
A  river  flowing  in  a  deep  narrow  trough. 

between  the  larger  streams  in  places  which  the  side  streams 
have  not  as  yet  been  able  to  reach.  Almost  the  entire 
surface  is  so  intricately  carved  into  drainage  lines  that 
wherever  water  falls  it  immediately  finds  a  downward  slop- 
ing surface.  The  main  stream  by  this  time  has  probably 
smoothed  out  most  of  its  falls  and  rapids  and  has  developed 
long,  smooth  stretches. 


180 


THE   WORK   OF    RUNNING   WATER 


Here  it  is  no  longer  cutting  down  its  trough,  but  has 
only  sufficient  slope  to  enable  it  to  bear  along  its  load  of 
waste.  It  here  deposits  upon  its  valley  floor  about  as 
much  as  it  takes  away.  In  this  part  of  its  course  a  river 
is  said  to  be  graded.  The  longer  a  river  flows  undisturbed 
by  any  deformation  of  its  valley,  the  fewer  falls  and  rapids 
it  will  leave  and  the  longer  will  be  its  graded  stretches. 
The  Missouri  River  near  Marshall,  Missouri,  is  an  excellent 
example  of  a  graded  river. 

Sometimes  a  stream  becomes  so  overloaded  with  detritus, 
which  it  has  acquired  in  a  steeper  part  of  its  extent,  or 


PLATTK  RIVER 

which  has  been  brought  to  it  by  tributaries,  that  it  is  con- 
tinually being  forced  to  deposit  some  of  its  load.  Thus  it 
silts  up  its  course  and  flows  in  a  network  of  interlacing 
shallow  channels.  The  Platte  as  it  crosses  the  plains  of 
Nebraska  is  an  example  of  such  an  overloaded  river. 

When  a  stream  swings  around  a  curve,  the  swiftest  part 
of  the  current  is  on  the  outside  of  the  curve  and  the  slowest 
on  the  inside.  A  river  that  is  carrying  about  all  the  load 
that  it  can,  on  passing  around  a  curve,  is  able  in  its  outer 
part  to  carry  more  than  before  and  cuts  into  the  bank, 
while  on  its  inner  part  it  flows  less  rapidly  and  is  able  to 


RIVER   DEVELOPMENT 


181 


carry  less,  thus  being  forced  to  drop  some  of  its  load.  As 
a  river  flows  along  its  graded  stretches,  eroding  -in  some 
places  and  filling  in  others,  it  broadens  its  valley  floor, 
leaving  at  the  border  of  its  channel  a  low  plain  which  in 
time  of  flood  may  be  covered  with  water. 

These   plains   are   very   fertile   and    are    usually    called 
"  bottom  lands  "  by  the  farmers.     They  are  often  unhealthy 


RIVER  EROSION 
Cutting  down  the  outer  side  of  the  curve  and  depositing  on  the  inner. 

because  of  floods  and  poor  drainage.  Where  the  water  in 
the  river  rises  rapidly  and  to  a  considerable  height,  it  is 
dangerous  to  inhabit  these  plains.  But  sometimes  these 
plains  are  so  fertile  that  they  are  densely  populated,  as 
the  plain  of  the  Ganges.  Such  a  river-made  plain  is  called 
a  flood  plain. 

If  a  river  once  begins  to  swing  on  its  valley  floor,  it  con- 
tinues to  do  so,  since  whenever  it  strikes  the  bank,  it  is 
deflected  toward  the  other  side,  and  is  made  to  move  in 
the  direction  of  the  opposite  bank  as  well  as  downstream. 


182  THE    WORK   OF   RUNNING   WATER 

The  windings  that  it  thus  assumes  on  a  flat  valley  floor  are 
roughly  S-shaped  and  are  called  meanders,  from  the  name 
of  a  river  in  Asia  Minor  which  was,  in  very  ancient  time, 
noted  for  having  such  swinging  curves.  The  size  of  these 
curves  will  be  proportional  to  .the  size  of  the  river. 

Great  rivers  like  the  Mississippi  have  a  swing  of  several 
miles,  while  a  small  stream  may  have  a  swing  of  only  a 


BOTTOM  LANDS 


few  feet  or  rods.     These  meanders  are  continually  chang- 
ing their  shape,  owing  to  the  cutting  and  filling. 

The  meanders  sometimes  become  so  tortuous  that  thej 
downstream  side  of  one  curve  approaches  the  upstream 
side  of  another  and  even  cuts  into  it,  thus  causing  the 
river  to  desert  its  curved  path  and  straighten  itself  at  this 
point.  The  old  deserted  winding  looks  something  like  an 
oxbow,  and  when  filled  with  water,  is  called  an  oxbow  lake. 


RIVER   DEVELOPMENT 


183 


Sometimes  the  meanders  are  artificially  straightened,  as 
has  been  done  in  the  lower  Rhine  valley,  and  much  arable 
land  reclaimed. 

In  time  of  flood,  when  a  river  spreads  over  its  flood  plain, 
the  velocity  of  the  water  is  checked  outside  the  channel 
and  some  of  the  sediment  it  carries  is  deposited.  The  most 


'    STREAM  MEANDERING  ON  ITS  FLOOD  PLAIN 

sudden  check  in  velocity  occurs  where  it  leaves  the  channel, 
so  more  material  will  be  deposited  here  than  elsewhere  on 
the  flood  plain.  The  banks  of  the  channel  will  thus  be 
built  up  more  rapidly,  and  the  flood  plain  near  the  river  will 
slope  away  from  the  channel  instead  of  toward  it. 

This  is  well  shown  in  the  lower  Mississippi,  where  the 
river  is  found  to  be  flowing  on  a  natural  embankment,  the 
side  streams  running  away  from  the  river  instead  of  into 


184 


THE    WORK   OF   RUNNING   WATER 


it.  In  some  places  the  embankment 
is  fifteen  or  twenty  feet  above  the 
rest  of  the  flood  plain.  These  natural 
levees,  as  they  are  called,  often  force 
the  tributary  streams  to  flow  for  long 
distances  upon  the  flood  plain  before 
they  can  enter  the  main  river.  The 
Yazoo  River  is  forced  to  flow  along 
the  flood  plain  some  200  miles  before 
it  can  enter  the  Mississippi. 
These  natural  levees  form  the  only 

available  sites  where  the  lower  river  towns  and  cities,  such 

as  New  Orleans,  can  be  built. 


OXBOW  LAKES 
A  stretch  of  the  Missis- 
sippi and  some  of  its 
abandoned  meanders. 


LEVEE  ALONG  LOWER  MISSISSIPPI 


Artificial  levees  are  often  built  to  keep  rivers  from  over- 
flowing their  flood  plains.  Such  are  the  high  levees  along 
the  Lower  Mississippi  and  Sacramento  Rivers. 


RIVER  DEVELOPMENT 


185 


Sometimes  the  flood  plain  of  the  main  river  is  built  up 
more  rapidly  than  the  tributaries  can  build  theirs,  so  that 
they  are  dammed  up  as  they  enter  the  flood  plain  of  the 
main  stream  and  form  a  series  of  fringing  lakes  along  its 
border.  A  fine  example  of  this  is  found  in  the  lower  course 
of  the  Red  River  of  Louisiana. 


AN  OLD  RIVEB 
This  river  has  done  its  work  and  has  completed  its  activities. 

When  a  river  has  graded  itself  and  built  its  flood  plain, 
its  own  active  work  consists  largely  in  carrying  off  the 
materials  brought  to  it  by  its  side  streams.  Although 
these  are  now  able  to  appropriate  no  new  territory  they 
continue  to  wear  down  the  country  and  round  oft"  the  divides 
till  the  whole  region,  unless  reelevated,  is  reduced  to  an 
almost  level  plain  with  its  entire  drainage  system  nearly 


186  THE   WORK   OF   RUNNING  WATER 

at  grade.  Most  of  the  material  now  carried  by  the  river 
is  in  solution,  and  there  is  but  little  erosion.  The  river 
has  accomplished  its  life  work,  it  has  borne  to  the  sea  all 
the  burden  it  has  to  bear,  its  labors  are  ended,  it  has  reached 
old  age. 

Rivers  in  Dry  Climates.  —  In  a  region  where  the  climate 
is  very  dry,  rivers  are  often  intermittent  in  their  flow. 
They  contain  water  only  after  rains.  Such  rivers  may 
dry  up  before  they  reach  any  other  body  of  water,  their 
water  entirely  evaporating  or  sinking  into  the  dry  soil. 
Their  development  is  therefore  somewhat  irregular. 

If  the  slopes  are  steep  and  there  is  little  vegetation  to 
protect  them  and  hinder  the  quick  run-off  of  the  water, 
rivers  flood  very  rapidly,  eroding  their  channels  and  wash- 
ing away  their  banks.  Where  they  descend  upon  level 
ground  they  silt  up  their  old  courses  and  acquire  new 
channels.  Thus  a  river  which  for  the  larger  part  of  the 
year  is  a  mere  brook  may  after  a  rain  become  a  devastat- 
ing torrent,  bursting  its  banks  and  'carrying  destruction 
to  settlements  and  farm  lands  along  its  course.  It  may 
even  change  its  entire  lower  course. 

Accidents  in  River  Development.  —  A  river  may  by  some 
accident,  such  as  the  melting  of  ice  during  the  Glacial 
Period,  have  had  its  supply  of  sediment  greatly  increased, 
causing  it  for  a  time  to  build  up  its  valley  floor  instead 
of  eroding  it,  thus  forming  a  filled  river  valley.  When 
the  supply  of  sediment  failed  the  river  began  cutting  down 
the  filled  valley,  leaving  terraces  along  the  sides  to  mark 
the  successive  levels  at  which  it  flowed.  Such  terraces  are 
often  very  prominent  along  our  northern  rivers. 

The  region  in  which  a  river  is  situated  may  be  elevated, 


ACCIDENTS  IN  RIVER  DEVELOPMENT          187 

thus  affecting  its  normal  development  and  beginning  a 
new  cycle  in  its  history.  The  elevating  may  take  place 
over  its  whole  drainage  area  or  only  over  a  part  of  it.  It 
may  take  place  at  any  time  during  the  history  of  the 
river.  If  it  takes  place  after  the  river  has  become  old 
and  is  meandering  on  its  flood  plain,  the  river  will  begin 
afresh  to  cut  down  its  valley.  But  as  its  meandering 


RIVER  TERRACES,  NORWAY 
The  river  is  now  cutting  down  its  former  plains,  leaving  terraces. 

course  has  been  established,  the  trench  that  it  now 
cuts  is  not  like  that  of  a  young  river,  but  is  a  meandering 
trench,  and  what  are  called  intrenched  meanders  are  formed. 
This  region  will  have  the  steep  V-shaped  valleys  charac- 
teristic of  a  young  region  and  the  well-developed  drain- 
age and  meandering  rivers  characteristic  of  a  mature 
region. 

It  was  the  intrenched  meandering  valley  of  the  Meuse 
River  at  Verdun  which  furnished  the  upland  spur  forti- 


188 


THE    WORK   OF   RUNNING   WATER 


fications  so  successfully  used  by  the  French  in  repelling  the 
German  march  up  the  valley. 

Not  only  may  a  river  be  elevated,  but  it  may  be  depressed. 
In  this  case  its  rate  of  erosion  is  diminished,  and  the  river 
becomes  marshy  where  the  grade  is  low.  Where  the  river 
valleys  approach  the  sea  they  will  be  submerged  or  drowned. 

These  drowned  river  valleys  form  some  of  the  finest 
harbors  on  the  coast.  San  Francisco  Bay,  Narragansett 


INTRENCHED  MEANDER 

Bay  and  New  York  harbor  are  examples  of  protected  harbors 
due  to  the  submergence  of  rivers.  The  mouth  of  the  Hudson 
was  formerly  some  seventy  miles  to  the  east  of  Long  Island, 
that  of  the  St.  Lawrence  to  the  east  of  Nova  Scotia.  In 
fact  the  Atlantic  coast  north  of  the  Hudson  furnishes  in- 
numerable examples  of  submerged  river  valleys. 

Delaware  and  Chesapeake  bays,  where  the  early  settlers 
each  had  a  nice  little  sea  inlet  instead  of  a  rough  wagon 


INTRENCHED  MEANDERS. 


DELTAS 


189 


road  as  his  means  of  communication  with  his  neighbors, 
are  fine  examples  of  submerged  river  systems.  These 
drowned*  river  valleys  enabled  the  early  settlers  to  penetrate 
easily  into  the  country,  and  determined  many  of  the  early 
settlements,  like  Philadelphia,  New  York,  and  Providence. 

Deltas.  —  When  a  river  enters  a  body  of  quiet  water, 
its  current  is  gradually  checked  and  it  deposits  its  material 


LAKE  BBIENZ  FROM  ABOVE  INTEKLAKEN,  SWITZERLAND 

A  rapidly  eroding  stream  at  the  right  has  built  a  great  delta  dividing 

the  ancient  lake  into  two  parts. 

in  somewhat  the  same  way  as  on  emerging  upon  a  flat 
country.  But  here  the  deposition  is  more  gradual  and 
the  slope  of  the  deposited  material  less  steep.  The  sedi- 


190  THE   WORK   OF   RUNNING   WATER 

ment,  too,  is  sorted  by  the  water,  and  the  finer  material  is 
carried  far  out  from  the  river  mouth.  Formations  of  this 
kind  are  called  deltas,  from  the  Greek  capital  letter  Delta 
(A),  which  has  the  shape  of  a  triangle.  Few  deltas  have 
this  ideal  shape,  but  there  is  a  general  correspondence  to  it. 
Deltas  have  rich,  fine-textured  soils  and  are  very  fertile. 
The  Nile  delta  during  all  history  has  been  noted  for  its 
fertility.  But  they  are  treacherous  places,  as  they  are  liable 
to  inundations  by  the  overflowing  of  the  river  at  time  of 
flood.  Because  they  are  pushed  out  into  the  sea,  they 
are  peculiarly  exposed  to  the  sweep  of  the  waves  in  great 
storms.  The  delta  of  the  Mississippi  is  more  than  200  miles 
long  and  has  an  area  of  more  than  12,000  square  miles.  The 
Po  in  historic  time  has  built  a  delta  more  than  14  miles 
beyond  Adria,  a  former  port  which  gave  its  name  to  the 
Adriatic  Sea. 

Inland  Waterways  and  History.  —  From  earliest  times 
rivers  have  played  a  most  important  part  in  the  world's 
history.  At  first  almost  all  human  movement  was  along 
river  valleys,  as  they  offered  the  easiest  routes  of  travel. 
Here,  too,  men  found  the  fertile  and  easily  worked  land  so 
necessary  in  their  primitive  agriculture.  Thus  their  settle- 
ments were  usually  placed  upon  the  banks  of  rivers.  In  war 
the  river  offered  a  means  of  defense,  as  the  Tiber  so  often 
did  to  Rome. 

Before  the  time  of  railways,  rivers  and  lakes  supplied 
almost  the  only  means  of  inland  commerce.  In  our  own 
country  the  hundred  and  fifty  miles  of  unobstructed  river- 
way  stretching  from  New  York  to  the  north  was  the  great 
road  from  Canada  and  the  Lakes  to  the  sea,  fought  for 
persistently  in  French  and  Indian  Wars  as  well  as  in  the 


INLAND   WATERWAYS  AND   HISTORY 


191 


Revolution.  If  in  the  Revolution  the  British  could  have 
obtained  control  of  the  Hudson,  they  would  have  effectu- 
ally separated  the  colonists  in  the  north  from  those  in  the 


OLD  FORT  DEARBORN 

Photographed  from  a  model  owned  by  the  Chicago  Historical  Society. 
This  fort  on  the  Chicago  River  fostered  the  trading  post  that  developed 
into  the  city  of  Chicago. 

south  and  would  probably  have  been  able  to  crush  each 
separately. 

The  Mississippi  River  served  for  years  as  the  only  artery 
of  transportation  from  the  interior  of  the  country  to  the 
sea.  When  Spain  held  the  mouth  of  this  river  and  Con- 
gress was  unable  or  unwilling  to  exert  itself  to  obtain  the 
privilege  for  American  boats  to  pass  to  the  sea,  it  seemed 
for  a  time  that  the  sturdy  colonists. along  the  Ohio  and 
Mississippi  would  either  form  an  independent  country 


192  THE   WORK   OF   RUNNING   WATER 

and  fight  for  the  privilege  or  else  in  some  way  ally  them* 
selves  with  Spain,  so  vital  to  them  was  the  need  of  this 
waterway.  In  the  Civil  War  vast  amounts  of  blood  and 
treasure  were  spent  in  fighting  for  the  control  of  this  river. 

The  majority  of  the  great  cities  of  this  country  owe  their 
beginnings  to  facilities  for  water  transportation.  Many 
of  them  were  first  established  as  forts  to  control  lines  of 
water  communication.  Some  of  the  most  important  of  them 
were  situated  near  portages  from  one  water  system  to  an- 
other. These  naturally  became  trading  posts;  and  as  the 
white  population  increased,  they  developed  into  important 
settlements. 

It  was  reasonable  that  these  places  should  be  among  the 
first  to  enjoy  railway  facilities.  If  it  happened  they  were 
situated  on  navigable  systems  that  tapped  regions  of  great 
natural  resources,  they  became  great  trading  cities.  If 
they  had  the  additional  good  fortune  to  be  in  the  midst  of 
great  coal  fields,  manufacturing  eventually  added  to  their 
prosperity.  If  in  addition  to  all  these  advantages,  they  lay 
in  the  natural  lines  of  "  long  hauls  "  of  developing  railway 
systems,  they  grew  with  astonishing  rapidity.  Railways 
have  also  mads  possible  the  building  of  great  "  inland 
cities,"  but  seldom  is  the  growth  of  such  cities  discussed 
without  the  expression  of  wonder  that  such  great  results 
should  be  achieved  in  spite  of  the  lack  of  water  trans- 
portation. 

The  Improvement  of  Waterways.  —  Two  thousand  years 
before  Christ  the  Babylonians  connected  the  Tigris  and 
Euphrates,  thus  showing  that  they  realized  the  commercial 
advantages  of  improved  waterways.  More  than  a  thousand 
years  ago  China  began  the  extending  of  her  waterways  by 


THE   IMPROVEMENT   OF  WATERWAYS  193 

building  a  canal  several  hundred  miles  long.  Since  then 
almost  every  civilized  nation  has  discovered  for  itself  the 
need  of  increasing  the  usefulness  of  its  natural  waterways 
and  has  built  artificial  channels  in  order  to  extend  cheap 
and  easy  facilities  for  transportation. 


SINGEL  CANAL,  AMSTERDAM 
A  canal  taking  the  place  of  the  usual  city  street. 

America  has  been  slower  to  awake  to  the  importance  of 
this  work  than  have  the  nations  of  western  Europe  with 
their  denser  populations.  Many  European  countries  are 
veritable  networks  of  improved  river  channels  and  canals. 
The  Seine  carries  the  greater  part  of  the  ocean  freight  to  and 
from  Paris.  The  Rhine  is  used  to  the  very  limit  of  its  navi- 


194 


THE    WORK   OF   RUNNING   WATER 


gable  course.  More  than  ninety-five  per  cent  of  the  Thames 
is  open  to  navigation.  A  canal  thirty-five  miles  long  and 
twenty-eight  feet  deep  conducts  ocean-going  vessels  to  and 
from  Manchester.  England  alone  has  over  two  thousand 
miles  of  canals. 

At  first  canals  were  built  entirely  for  inland  carriage,  but 
later  canals  of  international   importance   have   been  con- 


PANAMA 
An  example  of  man's  domination  over  nature. 

structed  to  shorten  the  routes  of  ocean-going  steamers. 
The  Suez  Canal  reduced  the  distance  by  boat  from  England 
to  India  by  about  one  third.  The  Kiel  Canal,  which  con- 
nects the  Baltic  with  the  North  Sea,  has  been  of  tremen- 
dous commercial  and  naval  importance  to  Germany.  The 
Panama  Canal  is  a  monument  to  American  efficiency.  It 
gives  easy  water  transportation  from  the  manufacturing 


THE   IMPROVEMENT   OF  WATERWAYS 


195 


cities  in  the  eastern  and  the  central  part  of  the  United  States 
to  the  Orient  and  to  the  western  coasts  of  North  and 
South  America.  It  also  allows  the  easy  concentration  of  the 
United  States  Navy  on  either  the  eastern  or  the  western 
coast. 

It  is  to  be  hoped  that  the  Erie  Canal,  connecting  the 
Hudson  River  and  the  Great  Lakes,  will  in  the  near  future 


CANAL 

Two  great  oceans  artificially  united. 

be  made  deep  enough  for  ocean-going  vessels.  Another 
project  of  great  importance  is  the  proposed  establishment, 
by  canals  and  dredging,  of  a  protected  waterway  from 
New  England  to  southern  ports.  A  network  of  inland 
waterways  connecting  Houston  and  New  Orleans  is  (Feb- 
ruary, 1919)  almost  completed.  By  extending  the  Chicago 
Drainage  Canal  and  dredging  the  Illinois  River  the  Great 


196  THE   WORK   OF   RUNNING   WATER 

Lakes  could  be  connected  by  navigable  channels  with  the 
great  Mississippi  system.  The  dredging  of  portions  of  the 
Mississippi  channel,  the  straightening  of  its  course,  and  the 
building  of  additional  permanent  levees  must  some  day  be 
accomplished .  Such  improvements  would  render  many  cities 
along  its  banks  veritable  inland  seaports. 

Waterways  such  as  these  would  relieve  the  great  freight 
congestions  that  now  so  frequently  occur  on  railroads  an.d 
that  will  become  more  frequent  with  the  increase  of  popula- 
tion. While  water  transportation  is  slower,  it  has  the  great 
advantage  of  being  much  less  expensive.  Many  such 
improvements  as  have  been  mentioned  have  been  strongly 
recommended  by  a  Commission  appointed  by  the  Federal 
Government. 

Sub-surface  Water  or  Ground  Water.  —  The  rain  that 
sinks  into  the  ground  descends  slowly  along  the  little  cracks 
or  between  the  particles  of  soil  until  it  reaches  a  point 
where  it  can  sink  no  further,  or  until  it  finds  an  opening 
through  which  it  can  flow  out  to  the  surface  at  a  point 
lower  than  where  it  entered.  Here  it  may  ooze  slowly  out, 
or  it  may  be  concentrated  in  a  spring. 

If  the  water  which  comes  to  the  spring  has  penetrated 
below  the  surface  far  enough  to  get  away  from  the  heating 
effect  of  the  sun,  it  will  be  comparatively  cool  when  it  again 
emerges,  and  it  will  form  a  cold  spring.  If,  however,  in 
the  region  where  the  spring  occurs  the  rocks  are  hot  at  the 
depth  to  which  the  water  penetrated  before  it  found  a  crack 
through  which  it  could  come  to  the  surface  of  the  land, 
then  it  will  become  heated  and  will  form  a  hot  spring. 

As  the  crust  of  the  earth  is  in  many  places  composed  of 
rocks  in  layers,  the  rain  often  falls  upon  the  top  of  a  folded 


SUB-SURFACE  WATER  OR  GROUND  WATER      197 

porous  rock  layer  below   which  is  a  rock   through  which 
it    cannot    penetrate.     The    water    will    then    accumulate 


HOT  SPRINGS  IN  THE  YELLOWSTONE  NATIONAL  PARK,  U.  S.  A. 

throughout  the  porous  rock.  If  this  rock  layer  in  another 
part  of  its  extent  is  overlaid  by  an  impermeable  layer,  its 
water  is  held  in  by  the  impermeable  rocks  above  and  below, 
and  so  is  under  hydraulic  pressure.  When  a  hole  is  made 


FIGURE  81 


in  the  upper  rock  layer  (Figure  81),  the  water  will  flow  to 
the  surface,  and  if  the  pressure  is  sufficient  it  may  gush  out 
of  the  hole. 


198 


THE  WORK  OF  RUNNING  WATER 


Borings  of  this  kind  form  what  are  called  artesian  wells. 
These  are  of  great  importance  in  many  regions  where  it  is 
difficult  to  obtain  sufficient  surface  water.  In  some  of  our 
western  states  the  water  from  artesian  wells  has  been  ob- 
tained in  sufficient  quantity  for  extensive  irrigation.  Al- 
though this  water  often  contains  minerals  in  solution,  it 

is  free  from  surface  con- 
tamination and  is  there- 
fore usually  healthful  for 
drinking. 

In  some  places  the  sur- 
face water  penetrates  into 
layers  of  rock  which  it 
can  dissolve,  such  as  salt 
or  limestone.  Here  it 
forms  caves  and  caverns, 
the  solid  material  which 
occupied  the  place  of  the 
cave  having  been  carried 
away  in  solution  by  the 
water.  There  are  thou- 
sands of  caves  of  this 
kind,  but  perhaps  the 
most  noted  in  this  coun- 
try is  Mammoth  Cave 
with  its  nearly  200  miles  of  underground  avenues  and 
grotesquely  sculptured  halls. 

Sometimes  the  top  of  one  of  these  caves  is  nearly  eroded 
away,  leaving  a  part  of  its  old  roof  standing  as  a  natural 
bridge,  such  as  the  natural  bridge  of  Virginia  or  of  Utah. 

Supplying  Water  to  Populous  Communities.  —  The  supply- 
ing of  water  to  large  communities  has  always  been  one  of 


FLOWING  ARTESIAN 


SUPPLYING  WATER  TO  POPULOUS  COMMUNITIES     199 

man's  great  problems.  Rome  received  its  water  supply  by 
aqueducts  from  nineteen  different  sources,  and  some  of 
these  aqueducts  were  in  use  for  fifteen  centuries.  The 
ruins  of  aqueducts  built  by  the  Romans  are  to-day  among 
the  most  picturesque  sights  of  the  Italian  and  Spanish  land- 
scapes. Eighteen  great  water  cisterns,  remarkably  well 
preserved,  are  the  only  remains  of  the  once  thriving  city  of 


STRETCH  OF  A  ROMAN  AQUEDUCT  NEAR  NiMEa,  FRANCE 

Carthage  on  the  North  African  coast.  Near  Tunis  may  be 
seen  a  stretch  of  the  ancient  aqueduct  that  brought  water 
to  these  cisterns  from  the  mountains  thirty-five  or  forty 
miles  to  the  south. 

Springs  and  shallow  wells  have  always  furnished  water 
to  favorably  situated  rural  districts  and  sometimes  to  small 
cities.  Only  in  recent  times  have  deep  wells  been  sunk 
and  water  lifted  from  great  depths.  Modern  large  cities 
have  seldom  found  supplies  of  water  from  underground 
sources  adequate  to  the  demands  of  manufacturing  and 


200  THE   WORK   OF   RUNNING   WATER 

sanitation,   although   for   many   years  London   and   Paris 

obtained  a  considerable  part  of  their  water  supply  from  these 

sources. 
Most  of  the  great  cities  of  the  world  are  largely  if  not 

wholly  dependent  on  near-by  rivers  and  lakes  for  the  water 

they  use.  Others  have 
gone  to  the  head- 
waters of  streams  in 
the  hills  or  mountains, 
have  conserved  these 
uncontaminated 
waters  in  huge  reser- 
voirs, and  have  con- 
structed great  pipe 
lines  to  conduct  the 
water  to  the  cities' 
mains.  The  Los  An- 
geles aqueduct  brings 
water  for  a  distance 
of  250  miles  down 
over  the  foothills  and 
through  the  desert. 
It  is  capable  of  sup- 
plying a  population  of 

A  PRIMITIVE  WATER  CARRIER  IN  MEXICO       2,000,000.        Such     an 

engineering  feat  makes 
the  ancient  aqueducts  look  almost  insignificant. 

How  Water  is  Delivered  through  Cities.  —  Ancient  cities 
had  not  the  advantages  of  modern  pressure  pumps.  They 
were,  therefore,  dependent  upon  gravity  to  bring  water  to 
them  from  sources  higher  than  the  community  served. 
Whenever  possible,  modern  cities  obtain  their  water  sup- 


HOW  WATER   IS   DELIVERED   THROUGH   CITIES     201 


plies  by  the  same  method.  But  the  modern  city  must  do 
more  than  merely  obtain  water ;  it  must  deliver  the  water 
to  every  part  of  the  city  and  to  the  top  floors  of  the  tallest 
buildings.  Where  cities  obtain  water  from  low  levels  they 
are  compelled  to  use  pumps,  or  pumps  combined  with  stand- 
pipes  or  elevated  reservoirs.  The  pressure  of  the  water  in 
these  standpipes  or  reser- 
voirs forces  the  water  to 
faucets  throughout  the 
city.  The  higher  the  sur- 
face of  the  water  is  above 
the  outlets,  the  greater 
will  be  the  pressure  (page 
146).  Largely  on  this 
account  water  from  a 
standpipe  or  elevated 
reservoir  has  a  weaker 
flow  from  faucets  on  upper 
floors  than  from  those  on 
lower  floors  of  the  same 
building. 

Friction  of  running 
water  against  the  pipes 
slows  it  up,  and  lowers 
the  pressure.  For  this  reason  a  reservoir  can  serve  only 
a  limited  district.  Large  cities  must  provide  many  such 
reservoirs.  The  necessity  of  furnishing  water  to  the  top 
floors  of  very  tall  buildings  and  of  fighting  fire  in  these  struc- 
tures has  compelled  large  cities  to  provide  high-pressure 
pumps  in  addition  to  reservoirs.  These  pumps  sometimes 
keep  the  water  in  the  mains  of  the  business  sections  at  a 
pressure  of  300  pounds,  or  even  more,  to  the  square  inch. 


A  STANDPIPE 

This  furnishes  water  under  high  pressure 
for  the  use  of  a  community. 


202 


THE  WORK  OF  RUNNING  WATER 


Almost  every  one  has  noticed  how  the  opening  of  a  faucet 
in  a  home  will  reduce  the  force  of  the  stream  from  a  garden 
hose.  This  illustrates  what  may  happen  on  a  larger  scale 
throughout  a  city  system.  The  larger  the  number  of  faucets 
running  at  one  time,  the  lower  the  pressure.  For  this 
reason,  most  cities  try  to  prevent  unnecessary  use  of  water 


FIRE-TUG  IN  ACTION 

The  "  Graeme  Stewart "  on  the  Chicago  River,  throwing  streams  of 
water  under  tremendous  pressure. 

in  homes  during  hours  when  business  districts  must  be 
served  and  protected  against  possible  fires.  This  is  why 
many  cities  forbid  the  sprinkling  of  lawns  during  the  busy 
hours  of  the  day. 

The  Vital  Importance  of  Pure  Water.  —  Roman  and  Greek 
writers  more  than  two  thousand  years  ago  emphasized  the 
advantages  of  a  pure  water  supply  to  a  city.  It  is  now 


THE  VITAL   IMPORTANCE   OF  PURE  WATER      203 

generally  recognized  that  a  modern  city  has  no  task  more 
vital  than  that  of  guarding  against  contaminated  water. 


WILSON  AVENUE  WATER  TUNNEL,  CHICAGO 

Photographed  during  construction.  This  tunnel  is  12  feet  in  diameter,  is 
hollowed  out  of  solid  rock  110  feet  below  the  surface  of  the  water, 
and  extends  eight  miles  from  the  pumping  station  on  the  north  shore 
to  the  crib. 

Those  communities  that  use  polluted  water  generally  have 
a  very  high  death  rate  from  typhoid  fever  and  from  other 
intestinal  diseases.  Moreover  the  industrial  efficiency  of 


204 


THE  WORK  OF  RUNNING  WATER 


a  population  is  greatly  reduced  by  sickness.  Cities  that 
receive  their  water  supplies  from  uncontaminated  up- 
lands have  a  tremendous  advantage. 

Cities  along  the  Great  Lakes  have  run  pipes  out  for  miles 
to  intakes,  or  cribs,  in  order  to  avoid  shore  contamination. 


ONE  OF  THE  CHICAGO  INTAKE  CRIBS 

In  time  of  heavy  storms,  the  sewage  from  a  city  sometimes 
contaminates  the  water  even  at  these  distant  intakes ;  but 
on  the  whole  the  supply  of  water  to  Great  Lakes  cities  is 
good.  Those  cities  which  receive  water  from  rivers  that  are 
constantly  being  polluted  by  the  sewage  of  communities 
farther  upstream  have  a  most  serious  problem,  even  though 
running  water  tends  somewhat  to  purify  itself.  In  many 
cases  this  problem  has  been  admirably  solved. 


A  TYPICAL  FILTER   PLANT  205 

St.  Louis,  for  example,  is  typical  of  many  cities  that  per- 
form marvels  in  transforming  muddy  river  water  into  clear, 
healthful  drinking  water.  The  Missouri-Mississippi  water 
as  it  enters  the  St.  Louis  intake  contains  mud  and  sand  in 
suspension;  coloring  matter  from  decaying  leaves,  as  well 


ST.  Louis  FILTER  PLANT 
This  building  of  reinforced  concrete  is  750  feet  long  by  135  feet  wide. 

as  mineral  matter,  in  solution ;  and  disease  bacteria.  As 
the  water  passes  slowly  through  settling  tanks  the  heavier 
sediment  falls  to  the  bottom  of  the  tanks.  Chemicals  are 
added.  Some  of  these  unite  with  the  coloring  matter,  and 
others  with  some  of  the  mineral  matter,  forming  chemical 
compounds  that  are  not  soluble  in  water.  These  compounds 
may  fall  to  the  bottom  of  settling  tanks  or  may  be  removed 


206 


THE  WORK  OF  RUNNING  WATER 


by  filtering  through  thick  beds  of  sand  and  gravel.     Finally 
small  amounts  of  chemicals  are  added  to  kill  the  harmful 


FIG.  82.  —  DIAGRAM  SHOWING  ST.  Louis  WATER  PURIFYING  PROCESS 
The  arrows  show  the  course  of  the  water  through  the  plant. 

bacteria,  and  the  pure  water  is  aerated  and  forced  through 
the  mains.  None  of  the  chemicals  used  makes  the  water 
harmful  to  drink  or  unpalatable  to  the  taste 


SUMMARY 

When  rain  falls,  some  of  it  evaporates ;  some  flows  away 
on  the  surface  of  the  land ;  some  sinks  into  the  ground,  to 
return  as  springs  or  wells.  The  water  which  flows  along  the 
surface  has  a  great  effect  upon  the  land.  It  forms  the 
little  streams  which  remove  the  surface  water,  the  huge 
rivers  which  drain  the  country  and  form  great  arteries  of 
trade,  and  the  beautiful  lake-reservoirs  which  hold  back 
floods  and  offer  easy  transportation  to  ships. 


SUMMARY  207 

But  most  important  of  all  is  the  erosion  caused  by  flowing 
water.  It  wears  down  the  land's  surface,  bears  away  and 
deposits  the  eroded  materials,  cuts  deep  trenches,  and  forms 
broad  valleys ;  it  fills  lakes  and  builds  great  deltas.  Falls 
and  rapids  furnish  water  power  for  manufactures. 

Rivers  that  have  not  yet  widened  their  valleys  and  still 
have  falls  and  rapids  are  called  young;  an  old  river  is  one 
whose  bed  has  been  worn  smooth,  and  which  has  built  for 
itself  a  broad  level  valley,  through  which  it  wanders,  doing 
little  if  any  erosive  work.  Rivers  sometimes  develop  flood 
plains  through  which  they  wander  in  S-shaped  meanders. 

If  the  region  of  a  river  becomes  elevated,  the  river  may  be 
revived,  and  if  it  is  a  meandering  river,  intrenched  mean- 
ders will  be  formed.  If  a  river  region  becomes  depressed, 
the  river  will  be  drowned.  These  drowned  river  valleys 
form  some  of  the  finest  harbors  in  the  world.  Many 
rivers  build  deltas  when  they  empty  into  bodies  of  quiet 
water. 

Rivers  have  always  played  a  most  important  part  in 
history,  because  river  valleys  offer  the  easiest  routes  of 
travel  and  furnish  most  fertile  soils.  Even  in  this  day  of 
railways,  the  largest  cities  of  the  world  owe  their  great  size 
to  combined  railway  and  water  transportation  facilities. 
So  important  is  adequate  water  transportation  that  the 
countries  of  Europe  have  developed  a  wonderful  network  of 
artificial  waterways  and  the  United  States  contemplates 
spending  millions  of  dollars  in  similar  enterprises. 

Springs  and  shallow  wells  furnish  water  to  favorably 
situated  rural  districts  and  to  some  small  communities. 
Most  great  cities  must  depend  on  surface  water.  Supplying 
water  to  populous  communities  is  a  most  difficult  under- 
taking. Water  must  be  piped  to  homes  and  office  buildings, 


208  THE   WORK   OF   RUNNING  WATER 

and  forced  to  high  levels.  If  the  water  is  liable  to  con- 
tamination, expensive  processes  of  purification  and  clarifi- 
cation are  installed  in  the  interest  of  public  health. 

QUESTIONS 

Trace  the  probable  journey  of  the  water  that  fell  near  your 
home  during  the  last  heavy  rain  until  it  reached  its  journey's  end. 

Describe  some  of  the  effects  of  running  water  that  you  have 
seen. 

Give  the  history  of  a  river's  development  in  a  moist  climate. 

How  do  rivers  in  dry  climates  differ  from  those  in  moist  climates  ? 

Describe  some  of  the  accidents  that  are  liable  to  happen  during 
a  river's  development. 

How  have  rivers  affected  history? 

What  has  been  man's  part  in  the  development  of  waterways? 

What  becomes  of  the  water  which  sinks  into  the  ground  ? 

How  is  water  supplied  to  the  cities  and  towns  near  your  home? 

Why  is  a  pure  water  supply  so  important  ? 


CHAPTER  VIII 

WEATHEE  AND  CLIMATE 

The  Warming  of  the  Atmosphere.  —  The  sun  trans- 
mits both  light  and  heat  to  the  surface  of  the  earth  through 
the  atmosphere.  On  the  top  of  a  high  mountain  the  tem- 
perature is  found  to  be  colder  than  on  the  lower  levels. 
The  amount  of  sun  radiation,  technically  called  insolation, 
that  falls  upon  a  given  surface  on  the  mountain  is  about 
the  same  as  that  which  falls  upon  an  equal  surface  in  the 
valley.  If  the  heating  effect  is 
less  it  must  be  due  to  something 
besides  the  number  of  heat  rays 
intercepted.  FIGUHZ  83 

In  the   spring  when   gardeners 

wish  to  hurry  the  growth  of  their  plants,  they  cover  them 
with  boxes,  the  tops  of  which  are  made  of  glass  (Figure  83). 
It  is  found  that  the  temperature  within  the  boxes  is  higher 
than  that  outside. 

The  high  temperature  heat  rays  coming  from  the  sun 
pass  readily  through  the  glass  and  are  absorbed  by  the 
ground  within  the  box,  raising  its  temperature.  The  ground 
continues  to  keep  warm  after  the  sun  ceases  to  shine  because 
the  heat  given  off  by  the  soil  under  the  box  cannot  readily 
pass  out  through  the  glass.  Thus  the  heat  of  the  sun  is  in 
a  certain  sense  entrapped  in  the  box  or  cold  frame. 
209 


210  WEATHER  AND   CLIMATE 

Now  the  atmosphere  does  for  the  earth  what  the  glass 
does  for  the  cold  frame.  The  rays  of  the  sun  pass  through 
the  transparent  atmosphere  and  warm  the  earth.  When 
the  earth  reflects  the  sun's  rays  or  gives  up  the  heat  it  has 
absorbed,  the  atmosphere  keeps  this  heat  from  immediately 
passing  off  into  space  and  leaving  the  surface  cold.  Where 
the  atmosphere  is  thin  as  on  mountains,  not  so  much  of 
heat  is  retained  and  therefore  their  surfaces  are  cold  and 
often  covered  with  snow.  Thus  the  atmosphere  acts  as  a 
blanket  and  keeps  in  the  heat  from  the  sun,  as  blankets  on 
a  bed  keep  in  the  heat  of  the  body. 

Clouds  help  to  hold  in  the  heat.  Farmers  know  that 
early  frosts  are  likely  to  come  on  clear  nights,  but  not  on 
cloudy  ones.  On  nights  when  there  is  likely  to  be  frost, 
plants  are  covered  with  pieces  of  paper,  smoky  fires  are 
built  around  cranberry  bogs,  and  orchards  are  smudged, 
in  order  to  blanket  in  the  heat. 

The  atmosphere  also  acts  as  a  sun-shield  and  protects  the 
surface  of  the  earth  from  the  consuming  heat  of  the  sun.  If 
there  were  no  atmosphere,  the  earth's  surface  would  become 
intensely  hot  during  the  day,  when  the  sun  shines  directly 
upon  it,  and  intensely  cold  at  night ;  so  that  life  could  not 
possibly  exist.  It  has  been  estimated  that  if  there  were 
no  atmosphere,  the  mean  temperature  of  the  earth's  surface 
during  the  day  would  be  350°  F.,  and  during  the  night  -123° 
F.  On  the  moon,  where  there  is  no  atmosphere,  there  can 
be  no  life  as  we  know  it. 

If  a  column  of  air  is  heated  it  becomes  lighter  and  the 
atmospheric  pressure  at  that  point  is  lessened.  The  cooler 
air  flows  in  below  and  forces  the  heated  air  to  rise.  Thus 
with  the  unequal  heating  of  different  places  on  the  earth's 
surface,  there  is  a  constant  tendencv  of  air  to  move  from 


THE  WARMING  OF  THE  ATMOSPHERE         211 


places  of  high  pressure  to  places  of  low  pressure ;  and  so 
the  air  is  constantly  in  motion,  tending  to  transfer  its 
heat  and  to  equalize  the  atmospheric  pressure.  The 
greater  the  difference  in  pressure  between  places,  the 
faster  the  movement  of  the  atmosphere  to  overcome  the 
difference. 

The  latitude  of  a  place  has  much  to  do  with  the  amount  of 
heat  it  receives.  As  the  sun  becomes  vertical  to  places 
north  of  the  equator,  the  length  of  the  day  in  the  northern 
hemisphere  increases, 
and  the  time  that  a 
place  is  in  the  sun- 
shine is  greater,  so 
that  it  receives  more 
heat  from  the  sun. 
On  the  21st  of  June 
all  points  within  23£° 
of  the  north  pole,  as 
at  North  Cape,  have 
twenty-four  hours  of 
sunshine  ;  and  the 
amount  of  heat  received  at  the  pole  during  these  twenty- 
four  hours  is  greater  than  that  received  at  the  equator, 
where  the  day  is  only  about  half  as  long.  But  so  much  of 
the  heat  is  absorbed  by  the  melting  of  ice  and  the  heating 
of  the  seas  that  have  grown  frigid  during  the  six  months  of 
night  that  the  sun's  heating  effect  on  the  atmosphere  is  rela- 
tively small. 

Although  the  latitude  of  a  place  has  much  to  do  with  the 
amount  of  heat  received,  there  are  also  many  other  things 
which  affect  its  temperature.  This  will  appear  when  we 
consider  that  Venice,  Italy,  with  its  mild  and  equable 


PICTURE  TAKEN  AT  MIDNIGHT  ON  NORTH 
CAPE 

The  sun  had  not  set  even  at  midnight. 


212 


WEATHER  AND   CLIMATE 


WINTER  SCENE  IN  VENICE 


climate,  is  in  almost 
the  same  latitude  as 
Montreal,  Canada. 

As  has  been  seen, 
the  height  above  the 
sea  makes  a  differ- 
ence with  the  tem- 
perature, since  'there 
is  less  thickness  of 
air  above  and  there- 
fore a  thinner  blanket 
to  hold  the  heat. 
Then,  too,  the  kind 
of  soil  affects  the 
temperature.  If  the 

soil  is  sandy  and  there  is  little  or  no  vegetation,  it  becomes 
rapidly  heated  in  the  daytime  and  radiates  back  the  heat 

into     the     air     very    K — ^ 

rapidly,  thus  making 
the  temperature  of 
the  air  near  the  sur- 
face very  hot  during 
the  day ;  while  at 
night,  when  the  sup 
is  not  adding  heat,  it 
rapidly  loses  the  heat 
acquired  during  the 
day,  and  so  the  tem- 
perature of  the  air 
becomes  low.  In  the 
daytime  on  great  WINTEK  SCENE  IN  MONTKEAL 

The  famous  Ice  Palace,  built  entirely  of 

sandy     deserts     the  blocks  of  ice. 


RECORDS  OF  WEATHER  CONDITIONS    213 

heat  is  almost  unbearable,  but  at  night  it  is  so  cold  that 
heavy  blankets  are  needed  to  keep  the  traveler  warm. 

The  nearness  to  the  sea  and  the  direction  of  the  wind 
also  greatly  affect  the  temperature  of  a  place.  In  some 
parts  of  the  earth  these  are  the  principal  causes  in  deter- 
mining the  temperature.  Thus  the  temperature  of  the 
atmosphere  at  any  place-  is  not  due  to  a  single  cause,'  but 
is  the  result  of  many  and  complex  causes  such  as  latitude, 
height,  direction  of  prevailing'  winds,  ocean  currents,  near- 
ness to  the  sea,  and  kind  of  soil. 


Graphic  Method  of  Showing  the  Temperature  of  a  Region. 
—  It  is  often  quite  essential  that  the  temperature  over  a 
considerable  region  should  be 
known  and  a  record  of  it  made 
and  preserved.  This  might  be 
done  by  taking  a  map  and  writ- 
ing their  temperatures  above  the 
different  places  marked  on  'the 
map.  This  would  make  a  map 
full  of  small  figures  and  very 
difficult  to  read. 


A    much    better    method    has  FIGURE  84 

been  developed  and  is  now  almost 

universally  used.  In  making  this  map  the  temperatures 
are  first  written  on  the  map  and  then  lines  are  drawn 
through  places  which  have  the  same  temperature.  These 
lines  are  called  isotherms  and  the  map  is  called  an  isothermal 
map.  By  the  use  of  such  a  map  it  is  possible  at  a  glance 
to  determine  the  temperature  prevailing  at  any  place 
and  to  see  the  relation  which  this  has  to  the  tempera- 
ture of  other  places  on  the  map.  As  a  rule  the  isotherms 


214 


WEATHER  AND   CLIMATE 


FIGURE  85 


are    not    drawn    for  each  degree,   but  only   for  each   ten 

degrees. 

When  the  map  has  been  constructed,  copies  are  made  in 

which  the  figures  are  left  off  and  only  the  isotherms  are 
preserved.  In  Figure  84  we  have 
a  plan  before  the  isotherms  are 
drawn,  and  in  Figure  85  after 
the  isotherms  are  drawn.  Figure 
86*  is  a  typical  isothermal  dia- 
gram. If  the  map  itself  were 
sketched,  it  would  be  an  iso- 
thermal map. 

Maps     recording      barometric 
conditions  are  made  in  the  same 

way  as  the  isothermal  maps,  only  their  lines  pass  through 

places  of   equal    barometric  pressure  instead    of   places  of 

equal  temperature.     These  lines  are  called  isobars. 
Weather  maps  are  prepared  by 

the  United  States  Weather  Bureau 

every  day,  on  which  are  both  the 

isotherms    and    isobars   for  that 

day.     The  data  for  these  maps 

are    telegraphed    each    morning 

from  stations  scattered   all  over 

the  settled  part  of  North  America. 

t* 

FIGURE  86 

Weather     Maps.  —  Expensive 

weather  bureaus  are  maintained  not  only  by  the  United 
States,  but  by  all  the  other  highly  civilized  countries  of 
the  world.  Records  are  kept  also  by  sea  captains  and  by 
other  observers  throughout  the  world,  and  these  are 
gathered  together  by  scientific  men  and  from  them  are 


CIRCULATION  OF  AIR 


215 


made  charts  of  the  weather  conditions  over  the  entire 
surface  of  the  earth.  Every  year  more  and  more  data  are 
being  collected  and  these  charts  are  becoming  more  and 
more  reliable. 

These  charts  are  of  great  value,  since  they  aid  in  the 
explanation  of  climatic  conditions  in  different  parts  of  the 
world.  The  results 
of  the  data  thus 
gathered  together 
have  been  of  untold 
service  to  commerce 
and  each  year  have 
saved  many  lives  and 
a  vast  amount  of 
wealth. 

Circulation  of  Air. 
—  The  atmosphere  is 
the  circulatory  medi- 
um of  the  earth,  as 
blood  is  for  the  ani- 
mal and  sap  for  the 
plant.  Without  it 

the  activities  of  the  earth  would  stagnate.  It  scatters  the 
seeds  of  plant  life  over  the  face  of  the  earth.  It  carries 
water  evaporated  from  the  sea  to  the  land,  replenishes  the 
underground  reservoirs  for  man's  use,  and  transports 
reserve  supplies  to  the  mountains  for  the  use  of  cities, 
for  power,  and  for  irrigation.  It  cools  the  hot  regions 
with  the  invigorating  breath  from  the  mountains  and  from 
the  uniformly  tempered  sea.  It  warms  the  cold  places  by 
bearing  to  them  the  heat  taken  from  the  warmer  ocean 


A  SAILING  VESSEL 

Both  the  sailing  vessel  and  the  steamship  are 
dependent  for  power  on  movements  of  the 
air  —  winds  and  drafts. 


216 


WEATHER   AND   CLIMATE 


OIL 


WATER 


FIGURE  87 


waters  and  from  the  parched  places  of  the  earth.  By  its 
movements,  it  keeps  the  very  fires  of  man's  factories  and 
engines  burning,  sweeps  the  smoke  and  foul  air  away  from 
his  cities,  and  bears  his  commerce  across  the  sea. 

Wind.  —  Experiment  75.  —  On  a  day  when  the  temperature  in 
the  room  is  considerably  higher  than  that  outside,  open  a  window 
at  the  top  and  bottom  and  hold  a 
strip  of  tissue  paper  in  front  of  the 
opening.  Is  there  an  air  current, 
and  if  so,  hi  what  direction  does  it 
move  at  the  top  and  at  the  bottom 
of  the  window  ?  What  causes 
"  drafts  "  in  a  room? 

Experiment    76.  —  Procure    two 

similar  dishes  about  15  cm.  high  and  5  or  6  cm.  in  diameter  with 
short  tubes  of  about  1  cm.  in  diameter  opening  out  from  near  the 
top  and  bottom.  Connect  the  bottom  tubes  of  the  two  dishes 
with  a  tightly  fitting  rubber  tube.  Do  the  same  with  the  top 
tubes.  Place  a  Hoffman's  screw  upon  each  of  the  rubber  tubes 
and  screw  it  tight  so  that  no  liquid  can  flow  through  either  tube. 
(If  part  of  each  rubber  tube  is  replaced  by  a  glass  tube, 
the  action  in  the  experiment  can  be  seen  to  better 
advantage.)  Fill  one  of  the  dishes  with  colored  water 
and  the  other  with  kerosene  or  some  light  oil. 

Release  the  Hoffman's  screw  upon  the  top  tube  and 
then  the  one  at  the  bottom.  Notice  carefully  what 
happens  as  the  lower  tube  is  allowed  to  open.  The 
dishes  are  not  now  filled  with  oil  and  water  respec- 
tively. In  the  transfer  of  the  liquids,  through  which 
tube  did  each  pass? 

Experiment  77.  —  Fill  a  convection  apparatus  with 
water,  putting  in  a  little  sawdust  and  mixing  it  well  with  the 
water.  Heat  one  side  of  the  tube  and  observe  the  convection 
currents  set  up. 

In  Experiment  76  the  interflow  from  one  dish  to  the  other 
is  due  to  the  fact  that  the  water  is  heavier  than  the  oil  and 


FIGURE  88 


WIND 


217 


runs  under  it  and  pushes  it  up  so  that  the  oil  overflows 
into  the  dish  that  the  water  has  left.  The  same  thing 
happens  in  the  atmosphere  when  from  any  cause  the  column 
of  air  above  one  place  becomes  heavier  than  that  above 
another  place.  There  will  be  under 
these  conditions  a  transfer  of  air, 
along  the  surface,  from  the  place 
where  the  pressure  is  greater  to  that 
where  it  is  less  great,  and  this  move- 
ment of  the  air  we  call  wind. 

The  wind  on  the  surface  of  the 
earth  is  not  usually  in  the  same 
direction  as  that  high  up.  The 
strength  of  the  wind  depends  upon 
differences  in  air  pressures.  As  the 
air  pressure  is  measured  by  the 
barometer,  the  wind  is  commonly 

In  this  common  appliance 

spoken  of  as  due  to  a  difference  in      the  heat  of  the  stove 


that  in  which  the  air  is 
caused  to  circulate  by 
the  heated  surface  of  the 
earth.  The  hot  water 
rises  to  the  top  of  the 
tank  from  where  the 
pressure  o»  the  cold 
water  in  the  supply 
cistern  will  cause  it  to 


barometric  pressure  or  to  the  bare- 
metric  gradient.  Winds  are  named 
from  the  direction  from  which  they 
come.  A  west  wind  is  a  wind  that 
blows  from  the  west. 

If  there  were  no  other  forces  that 
affected  the  movement  of  the  air, 
except  the  high  and  low  pressures, 

the  transfer  would  be  in  a  straight  line  from  one  place  to 
the  other,  and  it  could  always  be  told  in  what  direction  the 
high  and  low  pressures  were,  by  direction  of  the  wind. 
But  obstacles  like  mountains  and  hills  deflect  the  air 
currents.  Chief  among  other  causes  which  influence  the 
direction  of  air  movements  is  the  rotation  of  the  earth. 


218  WEATHER  AND   CLIMATE 

The  Effect  of  the  Earth's  Rotation  on  Winds.  —  Experiment 

78t  _  Revolve  a  globe  from  left  to  right  and  while  it  is  revolving  draw 
a  piece  of  chalk  from  the  pole  toward  the  equator.  Does  the  line 
as  marked  on  the  globe  follow  a  meridian?  What  is  its  genera! 
direction  in  lower  latitudes?  While  the  globe  is  revolving,  allow 
a  drop  of  water  to  run  from  one  pole  to  the  other.  Note  the  path 
it  takes. 

The  rotation  of  the  earth  affects  the  direction  of  move- 
ment of  all  bodies  free  to  move  over  its  surface.    Thus  if 


EFFECT  OF  PREVAILING  WIND  ON  GROWING  TREES 

a  current  of  air  starts  from  the  north  pole  to  flow  south,  it 
will,  as  it  goes  along,  tend  to  move  toward  the  right,  and  so 
when  it  reaches  middle  latitude  it  is  no  longer  moving 
south  but  southwest.  Why  this  is  so  can  be  fairly  well 
understood  if  the  conditions  of  this  moving  body  of  air 
are  considered. 


EFFECT  OF  EARTH'S  ROTATION  ON  WINDS     219 

As  the  earth  is  about  25,000  miles  in  circumference  and 
turns  on  its  axis  once  in  24  hours,  a  body  situated  at  the 
equator  is  carried  from  west  to  east  at  the  rate  of  about 
1000  miles  per  hour,  whereas  a  body  at  the  poles  simply 
turns  around  during  a  revolution.  Thus  as  we  go  on  the 
surface  from  the  poles  toward  the  equator,  each  point  has 
an  increasing  west  to  east  velocity. 

A  body  of  air,  not  being  attached  to  the  surface,  will 
have  this  west  to  east  velocity  imparted  to  it  very  slowly 
by  friction.  Thus  as  it  goes  from  higher  to  lower  lati- 
tudes, it  will  lag  behind  particles  on  the  surface  which  have 
this  west  to  east  velocity,  and  so  will  appear  to  have  an  east 
to  west  motion ;  just  as  to  a  person  riding  in  a  rapidly  mov- 
ing open  car  on  a  calm  day  there  seems  to  be  a  strong 
"  breeze."  (That  the  "  breeze  "  is  produced  by  the  motion 
of  the  car  and  not  by  movements  of  the  atmosphere  is 
shown  when  the  car  comes  to  a  standstill.)  The  north  to 
south  movement  of  the  air  combined  with  its  apparent  east 
to  west  movement  will  give  a  northeast-southwest  direction 
to  the  air  current. 

On  the  other  hand,  suppose  an  air  current  is  moving  from 
the  direction  of  the  equator  toward  the  north  pole.  It  has 
greater  velocity  toward  the  east  than  the  part  of  the  earth's 
surface  it  is  approaching,  and  so  instead  of  blowing  due 
north  it  takes  a  northeast  course.  It  can  be  seen  then  that 
whether  an  air  current  moves  from  the  north  pole  toward 
the  equator  or  from  the  equator  toward  the  north  pole,  it 
will  be  deflected  toward  the  right. 

It  can  be  proved  mathematically  that  all  freely  moving 
bodies  on  the  earth's  surface  are  deflected  toward  the  right 
in  the  northern  hemisphere  and  toward  the  left  in  the 
southern  hemisphere.  This  statement  is  called  Fen-el's  law. 


220 


WEATHER   AND   CLIMATE 


Planetary  Wind  Belts.  —  As  the  air  at  the  equator  re- 
ceives a  large  amount  of  heat,  it  becomes  warm  and  light, 
while  that  near  the  poles  is  cold  and  heavy.  The  air  would 
thus  have  a  constant  tendency  to  move  along  the  surface 
of  the  earth  toward  the  equator  and  in  an  upper  current 
from  the  equator  toward  the  poles,  just  as  in  the  dishes 
where  water  and  oil  were  connected.  But  this  direct 
movement  is  affected  by  the  rotation  of  the  earth  and  by 

certain  atmospheric  con- 
ditions, so  that  between 
25°  and  35°  both  north 
and  south  of  the  equator 
there  is  an  area  of  high 
pressure. 

From    these    areas    of 

u- u 

high  pressure  the  surface 
currents  move  both  to- 
ward the  equator  and 
toward  the  poles.  On 
account  of  the  earth's 
rotation  the  directions  of 
these  movements  are  not 

north  and  south  but  in  the  northern  hemisphere  northeast 
and  southwest.  Winds  of  this  kind  must  occur  on  every 
revolving  planet  having  an  atmosphere ;  hence  these  winds 
are  called  planetary  winds. 

As  the  rotation  of  the  earth  and  the  heating  of  the  air 
near  the  equator  are  conditions  that  do  not  change,  among 
the  most  permanent  things  about  our  planet  are  the  belts 
into  which  the  wind  circulation  is  divided.  The  change 
in  the  position  of  the  heat  equator,  —  the  belt  of  highest 
temperature,  —  due  to  the  apparent  movement  of  the  sun 


FIGURE  89. — WIND  BELTS  OF  THE 
EARTH 


WIND  BELTS  OF   THE   EARTH  221 

north  and  south,  modifies  the  conditions  in  these  wind 
belts  during  the  year.  The  planetary  winds  thus  modified 
are  sometimes  called  terrestrial  winds. 

Wind  Belts  of  the  Earth.  —  Near  the  heat  equator  where 
the  air  is  rising  there  is  a  belt  of  calms  and  light  breezes  called 
the  doldrums.  As  the  air  here  is  rising  and  cooling  (page 
125),  thus  losing  capacity  to  hold  moisture,  this  is  a  cloudy, 
rainy  belt  of  high  temperature  in  which  much  of  the  land 
is  marshy  and  the  vegetation  so  rank  and  luxuriant  that 
agriculture  is  exceedingly  difficult. 

Extending  north  and  south  of  the  doldrums  to  about  28° 
of  latitude  are  belts  in  which  constant  winds  blow  toward 
the  doldrum  belt  and  supply  the  air  for  the  upward  current 
there.  In  the  northern  hemisphere  these  winds  have  a 
northeast  to  southwest  direction  and  in  the  southern  hemi- 
sphere a  southeast  to  northwest  direction.  They  are  the 
most  constant  winds  on  the  globe  in  their  intensity  and  direc- 
tion, and  are  called  trade  winds.  Since  they  blow  from  a 
cold  region  to  a  warmer  region,  their  power  to  hold  mois- 
ture is  constantly  increasing  and  clouds  and  rains  are  not 
usual.  The  places  where  they  blow  are  dry  belts  and  in 
them  are  found  the  great  deserts  of  the  world. 

On  the  poleward  sides  of  the  trade-wind  belts  lie  the  areas 
of  high  pressure  already  referred  to.  These  are  called 
the  horse  latitudes  or  belts  of  tropical  calms  and  are  rather 
ill-defined.  The  air  is  here  descending  and  the  surface 
movements  are  light  and  irregular.  These,  like  the  dol- 
drums, are  regions  of  calms.  But  unlike  the  doldrums, 
they  are  dry  belts ;  since  the  descending  air  is  increasing 
in  temperature,  owing  to  adiabatic  heating  (page  125),  and 
thus  its  power  to  hold  moisture  is  increasing.  Therefore 


224  WEATHER   AND   CLIMATE 

the  tendency  of  the  atmosphere  in  these  belts  is  to  take  up 
moisture  rather  than  to  deposit  it. 

In  the  middle  latitudes  there  is  a  belt  of  irregular  winds 
which  have  a  prevailing  tendency  to  move  from  west  to  east 
or  northeast.  This  general  eastward  drift  of  the  air  is 
constantly  being  interrupted  by  great  rotary  air  movements 
having  a  diameter  of  from  500  to  1000  miles.  These  are 
called  cyclones  and  anti-cyclones.  In  this  region  of  the 
"  westerlies,"  since  the  air  tends  to  move  from  lower  to 
higher  latitudes,  an  abundance  of  moisture  is  usually  sup- 
plied. 

Cyclones  and  Anti-cyclones.  —  In  the  center  of  the  large 
storm  areas  called  cyclones,  the  barometric  pressure  is 
lower  than  that  of  the  surrounding  region,  and  so  they  are 
marked  "  Low "  on  the  weather  maps.  Into  these  low 
pressure  areas  the  air  from  all  directions  is  moving.  But 
the  winds  from  high  pressure  areas  do  not  blow  directly  into 
the  center  of  a  cyclone.  On  account  of  the  rotation  of  the 
earth,  any  wind  that  starts  toward  the  center  of  the  cyclone 
area  is  deflected,  in  the  northern  hemisphere  toward  the 
right ;  in  the  southern  hemisphere  toward  the  left  (page  219). 

For  example,  in  the  northern  hemisphere  the  wind  from  a 
point  north  'of  the  cyclone  center  will  be  deflected  to  the 
west ;  the  wind  from  the  south  will  be  deflected  to  the  east. 
Since  all  winds  blowing  toward  the  cyclone  area  veer  to 
the  right  of  the  cyclone  center,  they  produce  a  great  whirl 
in  a  direction  opposite  to  the  movement  of  the  hands  of  a 
clock.  (Figure  90.)  In  the  southern  hemisphere  the  cyclone 
rotates  in  a  direction  with  the  hands  of  a  clock. 

The  rate  at  which  the  wind  blows  varies  in  different  parts 
of  the  whirl,  but  is  never  very  great.  As  these  are  areas 


226  WEATHER   AND    CLIMATE 

of  ascending  and  cooling  air  they  are  storm  areas.  The 
extent  of  the  precipitation  varies  in  different  parts  of  a 
cyclone  according  to  the  direction  from  which  the  ascending 
air  has  come.  Note  the  direction  of  the  wind  and  the  rain- 
fall area  as  shown  on  the  map  (page  225).  Air  which  comes 
from  continental  interiors  is  dry,  while  that  from  great  water 
areas  contains  much  moisture,  much  of  which  it  deposits 
when  it  cools  by  ascending  (page  125).  To  these  cyclones 

is  due  the  larger  part  of 
the  rain  which  falls  in 
middle  latitudes. 

The  anti-cyclone  is  just 
the  opposite  of  a  cyclone. 
The   center   of    an    anti- 
cyclone is  a  place  of  clear 
FIGURE   90.  —  DIRECTIONS  OF  WINDS  IN      ,  j     i  •   i 

AN  ANTI-CYCLONE  AND  IN  A  CYCLONE        sky     and     high     pressure. 

The    air    movement     is 

slowly  downward  and  outward  from  the  center.  (Figure 
90.)  These  winds  are  dry,  cool,  and  gentle. 

Paths  of  Cyclonic  Storms  across  the  United  States.  —  If 
you  will  watch  the  weather  maps  for  several  days  in  succes- 
sion, you  will  find  that  cyclones  or  "  Lows  "  move  in  a  general 
eastward  direction.  The  accompanying  map  shows  the 
paths  of  a  large  number  of  cyclonic  storms  across  the  United 
States.  It  will  be  seen  from  this  that  although  these  paths 
vary  considerably,  yet  the  general  direction  is  a  little  north 
of  east.  The  movement  of  cyclones  is  in  the  general  direc- 
tion -of  the  prevailing  winds  of  the  middle  latitudes. 

In  winter  time  the  average  rate  of  motion  of  the  cyclone 
across  the  continent  is  about  800  miles  a  day,  while  in  summer 
it  is  only  about  500.  The  velocity  of  the  wind  in  the  cyclone 


PATHS  OF  CYCLONIC  STORMS 


227 


itself  is  also  much  greater  in  winter  than  in  summer,  since 
the  difference  in  pressure  between  the  high  and  the  low 
areas  is  much  greater.  The  changes  in  temperature  as  the 
storms  pass  are  greater  in  winter  than  in  summer  since  the 
regions  from  which  the  northerly  and  the  southerly  winds 
flow  in  toward  the  center  of  low  pressure  vary  more  in  their 
temperatures. 

During  the  summer  months  people  who  live  in  the  Missis- 
sippi Valley  usually  look  to  the  south  or  southwest  for  the 


AVERAGE  DAILY  MOVEMENTS 


clouds  which  bring  rainstorms.  From  this  direction  come 
the  moist  northerly  blowing  winds  (deflecting  toward  the 
east)  from  the  Gulf  of  Mexico.  The  heaviest  rain  is  always 
in  the  fore  part  of  the  eastward  moving  cyclone.  The  mois- 
ture laden  winds  coming  from  a  warmer  to  a  colder  region 
and  being  forced  upward  in  the  cyclone  deposit  some  of 
their  moisture.  In  the  western  part  of  the  cyclone  are  the 
winds  blowing  from  northerly  points.  These  come  from 


228  WEATHER   AND   CLIMATE 

cooler  into  warmer  regions  and  their  capacity  for  moisture 
is  increasing.  As  the  center  of  the  cyclone  passes,  therefore, 
the  clouds  generally  begin  to  clear  and  the  atmosphere  begins 
to  cool. 

Sudden  Weather  Changes.  —  In  middle  latitudes  there 
often  occur,  particularly  in  winter,  sudden  changes  in  the 
temperature  of  20°  or  more  in  a  few  hours.  In  our  own 
country,  if  the  temperature  falls  20°  or  more  in  twenty-four 
hours,  reaching  a  point  lower  than  32°  F.  in  the  north  or  lower 
than  40°  in  the  south  it  is  known  technically  as  a  cold  wave, 
and  there  is  a  special  flag  (Figure  91)  displayed  by  the 
Weather  Bureau  to  indicate  the  approach  of 
such  a  change. 

When  these  waves  extend  over  the  southern 
part  of  the  country,  they  are  very  destructive 
to  the  orange  groves  and  delicate  crops  and  are 
known  as  "  freezes."  A  notable  freeze  of  this 
kind  occurred  in  1886  and  did  tremendous 
damage  to  the  orange  groves  of  Florida.  So  great  was  the 
effect  upon  this  important  industry  throughout  the  orange 
belt  that  for  years  afterward  the  "  freeze  "  was  the  date 
from  which  events  were  reckoned. 

If  the  northwesterly  wind  which  brings  on  the  cold  wave 
is  accompanied  by  snow,  it  is  called  a  blizzard,  and  on  the 
plains  and  prairies,  where  the  wind  has  a  clear  sweep,  it 
is  much  dreaded.  Cattle  and  men,  when  caught  in  it,  fre- 
quently perish.  In  southern  Europe  the  coldest  winds 
are  from  the  Siberian  plains  and  are  therefore  northeasters. 
In  the' United  States  the  cold  area  is  at  the  southwest  and 
rear  of  the  cyclone,  whereas  in  Europe  it  is  at  the  north 
and  front. 


THUNDERSTORMS  229 

When,  instead  of  the  strong,  cold,  northwest  winds  which 
blow  into  the  rear  of  a  cyclonic  area  and  in  the  colder  seasons 
may  produce  a  cold  wave,  there  is  a  prolonged  movement 
of  highly  heated  air  from  the  south  into  the  front  of  the 
low  pressure,  as  sometimes  occurs  during  the  warm  months, 
the  "  hot  spells  of  summer  "  are  caused.  The  air  is  sultry, 
exceedingly  hot  and  oppressive.  Sunstrokes  and  prostra- 
tions from  heat  are  common.  The  "  hot  winds  "  of  Texas 
and  Kansas,  the  Santa  Ana  of  lower  California  and  the 
siroccos  of  southern  Italy  are  intensified  examples  of  these 
winds.  All  sudden  weather  changes  of  this  kind  are  due  to 
atmospheric  conditions  related  to  areas  of  low  pressure. 

Thunderstorms.  —  Often  on  a  hot,  sultry  summer  after- 
noon large  cumulus  clouds  are  seen  to  rise  and  spread  out 
till  they  cover  the  sky.  The  wind  soon  begins  to  blow 
quite  strongly  toward  the  cloud-covered  area,  the  clouds 
moving  in  a  direction  opposite  to  the  surface  wind.  As 
the  storm  clouds  approach,  a  violent  blast  of  wind,  often 
called  the  thundersquall,  blows  out  from  the  front  of  the 
storm.  Soon  flashes  of  lightning  appear  and  thunder  is 
heard.  As  the  storm  comes  nearer,  the  rain  begins  to  descend 
and  for  a  short  time,  usually  about  half  an  hour,  it  rains 
heavily.  Then  the  clouds  roll  away  and  the  sky  becomes 
clear  with  perhaps  a  rainbow  to  heighten  the  beauty  of  the 
clearing  landscape. 

Thunderstorms  are  caused  by  hot  moist  air  rising  over 
certain  areas  and  causing  an  updraft,  which  is  increased 
by  the  inflow  and  upward  movement  of  air  from  the  sur- 
rounding regions.  The  condensation  of  the  moisture  in  the 
rising  air  quickly  forms  clouds,  and  these  become  charged 
with  electricity.  As  the  electrical  charge  increases,  dis- 


230  WEATHER  AND   CLIMATE 

charges  take  place  which  cause  lightning  flashes.  These 
discharges  occur  along  the  lines  of  least  resistance  and  are 
often  very  irregular  and  forked.  As  tall  objects  are  likely 
to  offer  good  paths  for  the  discharge,  it  is  safest  to  keep  away 
from  trees  and  walls  during  a  thunder-storm. 

The  air  becomes  greatly  agitated  by  the  lightning  dis- 
charges and  makes  us  aware  of  this  by  the  noise  of  the 
thunder,  just  as  the  agitation  of  the  air  caused  by  the  dis- 
charge of  a  gun  is  made  apparent  to  us  by  what  we  call 
the  noise  of  the  report.  The  flash  of  lightning  reaches  the 
eye  almost  instantly  after  the  electrical  discharge;  but 
since  sound  travels  at  the  rate  of  about  a  mile  in  five  seconds, 
there  is  often  a  noticeable  lapse  of  time  between  the  ap- 
pearance of  the  flash  and  the  sound  of  the  thunder.  The 
noise  from  different  parts  of  the  discharge  will  reach  us  at 
different  times,  and  to  this  and  the  echoing  from  clouds  or 
hills  is  due  the  roll  of  the  thunder.  To  tell  in  miles  the 
approximate  distance  of  the  flash,  one  has  only  to  divide  by 
five  the  number  of  seconds  that  elapse  between  the  appear- 
ance of  the  flash  and  the  noise  of  the  thunder. 

Frequently  in  the  evening  flashes  called  heat  lightning 
are  seen  near  the  horizon.  These  are  due  to  the  reflection 
on  clouds  of  flashes  of  lightning  in  a  storm  which  is  below 
the  horizon.  Thunder-storms  occur  sometimes  in  winter. 
They  are  very  prevalent  in  the  tropics. 

Tornadoes  and  Waterspouts.  —  Sometimes  causes  like 
those  which  produce  a  thunder-storm  are  so  strongly  de- 
veloped that  the  indraft  is  exceedingly  violent  and  a  furious 
whirling  motion  is  produced.  Such  storms  are  called 
tornadoes.  The  warm,  moist  air  rises  rapidly  and  spreads 
out  into  a  funnel-shaped  cloud  with  the  vertex  hanging 


RAINFALL  AND   ITS  MEASUREMENT 


231 


toward  the  earth.  In  the  center  of  the  whirl  the  air  pres- 
sure is  much  diminished  and  the  velocity  of  the  inrushing 
whirling  wind  is  tremendous,  being  often  sufficient  to  de- 
molish all  obstacles 
in  its  path. 

The  length  of  the 
path  swept  over  by 
a  tornado  is  rarely 
over  thirty  or  forty 
miles  and  the  width 
generally  less  than 
a  quarter  of  a  mile. 
The  rate  of  progress 
in  the  Mississippi 
valley  is  from  twenty 
to  fifty  miles  an 
hour,  usually  in  a 
northeasterly  direc- 
tion. These  storms 
are  often  wrongly 
called  cyclones. 
When  storms  of  this 
kind  occur  at  sea,  a 
water  column  is  formed  in  the  funnel-shaped  part  of  the 
storm  and  they  then  receive  the  name  of  waterspouts. 

Rainfall  and  Its  Measurement.  —  Experiment  79.  —Place  a 
dish  with  vertical  sides  in  a  large  open  space  so  that  the  rim  is  hori- 
zontal and  at  a  height  of  about  one  foot  above  the  ground.  Fasten 
the  dish  so  that  it  cannot  be  overturned  by  the  wind.  After  a 
rain,  measure  the  water  that  has  collected  in  the  dish  to  the  smallest 
fraction  of  an  inch  possible.  This  will  be  the  amount  of  rainfall 
for  this  storm. 


A  TORNADO 
Notice  the  funnel-shaped  cloud. 


232 


WEATHER   AND    CLIMATE 


The  amount  of  rainfall  during  the  year  varies  greatly 
in  different  places.  It  amounts  to  nothing  or  only  a  few 
inches  over  some  regions,  as  in  parts  of  Peru  where  rain 
falls  only  on  an  average  of  once  in  five  years.  But  in  the 
Khasi  Hills  region  of  India  it  has  been  known  to  be  over 
600  inches ;  and  over  40  inches,  or  about  the  average  yearly 


EFFECTS  OF  A  TORNADO 

The  iron  windmill  was  blown  across  the  cellar  and  protected  the  people 
who  had  fled  there  for  safety. 

rainfall  for  the  eastern  United  States,  has  been  known  to 
fall  in  24  hours. 

The  rainfall  in  different  parts  of  the  earth  has  been  care- 
fully measured  and  maps  showing  its  average  amount 
prepared.  As  agriculture  is  largely  dependent  upon  the 
amount  of  rain  and  the  season  of  the  year  in  which  it 
falls,  these  maps  tell  much  about  the  relative  produc- 
tivity of  different  regions  of  the  earth.  An  annual  total 
of  eighteen  or  more  inches  is  necessary  for  agriculture; 


RAINFALL  AND  ITS  MEASUREMENT 


233 


and  this  must  be  properly  distributed  throughout  the 
year. 

On  examining  a  map  of  the  mean  annual  rainfall  (page 
235),  we  see  that  there  are  large  areas  where  it  is  not  sufficient 
for  agriculture  with- 
out irrigation.  Such 
areas  are  within  the 
belts  of  dry  winds 
or  in  continental  in- 
teriors far  from  large 
bodies  of  water.  The 
rain-bearing  winds 
coming  from  the  wa- 
ter are  forced  to  rise 
and  cool  so  that  their 
moisture  is  deposited 
before  reaching  these 
interior  regions. 

The  rainfall  of  a 
place  depends 
largely  :  (1)  upon  its 
elevation,  since  most 
of  the  rain-bearing 
clouds  lie  at  low  alti- 
tudes ;  (2)  upon  the 
direction  and  kind  of 

winds  that  blow  over  it ;  and  (3)  upon  the  elevation  of  the 
land  about  it.  The  sides  of  mountains  toward  the  direction 
from  which  the  rain-bearing  winds  approach  will  be  well 
watered,  while  the  opposite  side  may  be  a  barren  desert. 

A  cylindrical  vessel  having  vertical  sides,  called  a  rain 
gauge,  is  used  to  determine  the  amount  of  rain.    It  is  placed 


WATERSPOUT  SEEN  OFF  THE  COAST  OF 
NEW  ENGLAND 


234  WEATHER  AND   CLIMATE 

in  an  open  space  away  from  all  trees  and  buildings  and 
after  each  rain  the  amount  collected  is  measured.  Snow 
is  melted  before  it  is  measured.  As  a  rule  eight  or  ten 
inches  of  snow  make  an  inch  of  rain. 

If  the  temperature  is  below  the  freezing  point,  32°  F., 
when  condensation  takes  place,  the  moisture  of  the  air 
will  form  into  a  wonderful  variety  of  beautiful  six-rayed 
crystals.  These  gather  into  feathery  snowflakes,  which 
float  downward  through  the  air  and  often  cover  the  ground 
with  thick  layers  of  snow.  Although  snow  is  itself  cold,  yet 
it  keeps  in  the  heat  of  the  ground  which  it  covers,  so  that 

in  cold  regions  soil 
which  is  snow-covered 
does  not  freeze  as  deeply 
as  that  without  snow. 
Therefore,  to  keep  water 
pipes  from  freezing,  it  is 

MAGNIFIED  SNOW  CRYSTALS 

not  necessary  to  bury 

them  as  deeply  in  localities  where  snow  is  abundant  as  in 
places  equally  cold  where  snow  seldom  falls. 

If  raindrops  become  frozen  into  little  balls  in  their  passage 
through  the  air,  they  fall  as  hail.  Hail  usually  occurs  in 
summer  and  is  probably  caused  by  ascending  currents  of 
air  carrying  the  raindrops  to  such  a  height  that  they  are 
frozen  and  often  mixed  with  snow  before  they  fall.  Some- 
times hailstones  are  more  than  a  half  inch  in  diameter. 
They  occasionally  do  great  damage  to  crops  and  to  the  glass 
in  buildings. 

Sleet  is  a  mixture  of  snow  and  rain. 

Rainfall  of  the  United  States.  —  An  examination  of  a 
rainfall  map  of  the  United  States  will  show  that  the 


RAINFALL  OF  THE  UNITED  STATES  235 


236 


WEATHER   AXD    CLIMATE 


distribution  of  rainfall  can  readily  be  divided  into  four 
belts  which,  although  gradually  shading  the  one  into  the 
other,  are  yet  quite  distinct.  These  belts  may  be  called 
the  north  Pacific  slope,  the  south  Pacific  slope,  the  western 
interior  region,  and  the  eastern  region. 

In  the  north  Pacific  coast  region  the  storms  of  the  "  wester- 
lies "  are  common,  particularly  in  winter,  when  the  westerly 

winds  are  strong  and 
stormy.  The  yearly 
rainfall  here  amounts 
to  about  seventy 
inches. 

From  central  Cali- 
fornia south  the  rain- 
fall of  the  Pacific 
slope  decreases  until, 
in  southern  Califor- 
nia, there  is  almost 
no  rain  in  summer 
and  the  entire  rain- 
fall for  the  year  aver- 
ages about  15  inches. 
The  high-pressure 

area  °f  tne  dry  tropi- 
cal  calm  belt  moves 

sufficiently  far  north 

in  summer  to  take  this  region  out  of  the  influence  of  the 
wet  westerlies  and  into  that  of  the  drier  belt. 

The  western  interior  region,  extending  from  the  Cas- 
cade and  Sierra  Nevada  mountains  to  about  the  100th 
meridian,  is  dry  over  the  larger  part  of  its  surface,  since 
the  winds  have  deposited  most  of  their  moisture  in  pass- 


SALMON  RIVER  DAM,  IDAHO 
A  typical  irrigation  dam  in  the  United  States. 


WEATHER  FORECASTING  237 

ing  over  the  mountains  to  the  west.  On  the  mountains 
and  high  plateaus,  however,  there  is  a  considerable  fall  of 
rain,  as  the  winds  are  cooled  sufficiently  in  passing  over 
these  to  deposit  their  remaining  moisture.  In  most  of 
this  region,  as  also  in  southern  California,  irrigation  must  be 
resorted  to  if  agriculture  is  to  succeed.  The  fall  of  rain 
on  the  mountains  and  high  plateaus  supplies  rivers  of 
sufficient  size  to  furnish  water  for  extensive  irrigation, 
and  so  a  considerable  part  of  the  area  which  is  now  prac- 
tically a  desert  will  in  the  future  be  reclaimed  for  the  use 
of  man.  The  government  is  at  present  engaged  in  extensive 
irrigation  work  in  this  territory. 

From  about  the  100th  meridian  to  the  Atlantic  Ocean 
there  is  a  varying  rainfall,  but  it  is  as  a  rule  sufficient  for 
the  needs  of  agriculture.  It  gradually  increases  toward 
the  east,  moisture  being  supplied  plentifully  from  the  Gulf 
of  Mexico  and  the  Atlantic  Ocean  by  the  southerly  and 
easterly  winds.  The  rainfall  is  wrell  distributed  through- 
out the  year  and  averages  from  thirty  to  sixty  inches. 

Weather  Forecasting.  —  The  data  'necessary  for  fore- 
casting the  weather  are  telegraphed  to  the  Weather  Bureau 
stations  every  day,  and  a  record  of  them  placed  on  the 
weather  map.  The  observations  recorded  on  these  maps 
furnish  the  forecasters  with  all  the  information  obtainable 
as  to  what  the  weather  of  the  future  is  to  be.  It  has  al- 
ready been  stated  that  the  dominant  cause  of  our  weather 
conditions,  in  middle  latitudes,  is  the  eastward  movement  of 
cyclones  and  anti-cyclones. 

If  the  direction  and  rate  of  motion  of  these  can  be  deter- 
mined the  weather  of  those  places  which  are  likely  to  come 
under  their  influence  can  be  foretold  with  a  good  deal  of 


238  WEATHER   AND   CLIMATE 

accuracy.  If  a  cyclone  were  central  over  the  lower  Mis- 
sissippi valley  with  an  anti-cyclone  to  the  west  of  it,  we 
should  expect  that  the  southerly  and  southeasterly  winds 
and  rains  to  the  east  and  southeast  of  the  Mississippi  would 
gradually  change  to  fair  weather  and  westerly  winds  with 
increasing  cold,  as  the  cyclonic  area  was  replaced  by  the 
anti-cyclonic. 

The  rate  at  which  the  change  would  take  place  would 
depend  upon  the  rapidity  of  the  movements  of  the  two 
areas  of  high  and  low  pressure,  and  the  order  of  change  in 
the  direction  of  the  winds  would  depend,  for  any  place, 
upon  the  directions  taken  by  the  centers  of  these  areas. 
The  direction  of  movement  and  the  rapidity  of  movement 
of  the  cyclonic  areas  are,  therefore,  two  of  the  chief  factors 
which  enter  into  the  prediction  of  the  weather.  There  is 
usually  an  increase  in  the  intensity  of  the  storm  as  the 
Atlantic  coast  is  approached. 

Climate.  —  The  average  succession  of  weather  changes 
throughout  the  year,  considered  for  a  long  period  of  years, 
constitutes  the  climate.  Thus,  if  the  average  temperature 
of  a  place  throughout  the  year  has  for  a  long  period  been 
found  to  be  high,  and  the  rainfall  large  and  uniformly 
distributed,  the  place  is  said  to  have  a  hot  and  humid  climate. 
The  climate  is  a  generalized  statement  of  the  weather. 
Two  places  may  have  the  same  average  temperature  through- 
out the  year  without  having  the  same  climate,  as  in  one  the 
temperature  may  be  quite  uniform  and  in  the  other  very  high 
at  one  season  and  very  low  at  another.  Many  factors  enter 
into  the  making  up  of  a  comprehensive  statement  of  climate. 

Effect  of  Mountains  on  Climate.  —  All  over  the  world 
where  people  have  the  money  and  the  leisure  they  are 


EFFECT  OF  MOUNTAINS  ON  CLIMATE 


239 


accustomed  to  go  either  to  the  mountains  or  the  seashore 
in  summer  in  order  to  get  where  it  is  cooler.  They  might 
for  the  same  purpose  travel  northward  in  the  northern 
hemisphere,  but  they  would  need  to  go  many  times  as  far 
to  get  the  same  fall  of  temperature. 

In  summer  one  must  ascend  a  mountain  on  an  average 
about  300  feet  vertically  to  get  a  mean  fall  of  1°  F.,  whereas 


TOP  OF  PIKE'S  PEAK  IN  SUMMER 
Notice  the  snow  and  the  rocks  broken  up  by  freezing  water. 

one  must  travel  over  60  miles  north  to  get  the  same  change. 
In  winter  one  must  ascend  farther  on  the  mountain  and  travel 
not  so  far  north,  to  get  a  change  of  a  degree.  As  one  ascends 
a  mountain  it  grows  colder  and  colder.  In  ascending  a 
high  mountain  in  the  tropics  one  passes  through  all  the 
changes  in  climate  which  one  would  pass  in  going  from  the 
equator  toward  the  poles. 

As  already  stated,  high  mountains  also  affect  the  climate 
of  the  country  near  them.     The  windward  side  of  moun- 


240 


WEATHER  AND  CLIMATE 


tains  is  moist,  since  the  moisture  in  the  air  is  condensed  in 
rising  over  them.  On  the  lee  side  the  country  is  dry,  as 
the  air  which  moves  over  it  has  already  been  deprived  of 
its  moisture. 

The  country  on  the  lee  side  will  also  be  subject  to  hot, 
dry  winds  like  the  chinook  winds  of  the  eastern  Rockies 
and  the  foehn  in  Switzerland.  As  the  moist  winds  pass 


POPOCATEPETL 
A  snow-covered  mountain  in  the  tropics. 

over  the  mountains  their  moisture  is  condensed.  This 
raises  their  temperature  so  that  it  is  above  what  it  would 
normally  be  at  the  altitude  reached.  As  these  winds  come 
down  on  the  lee  side  of  the  mountain,  the  air  is  compressed 
and  thus  heated  (page  125)  so  that  on  this  side  it  is  consid- 
erably warmer  at  the  same  altitude  than  on  the  windward 
side.  Thus  high  mountains  affect  not  only  the  rainfall, 
but  the  temperature  changes  of  the  region  round  about. 


CLIMATE   OF   LAKE   AXD   OCEAN   SHORES       241 


Effects  of  Large  Bodies  of  Water  on  Climate.  —  We  have 
learned  that  dark,  rough  surfaces  absorb  heat  more  rapidly 
than  smooth,  light,  highly  reflecting  surfaces.  We  have 
also  learned  that  a  great  deal  of  heat  is  required  to  raise 


MID-OCEAN 
Showing  the  constant  motion  of  the  water. 

the  temperature  of  water  one  degree  —  nine  times  as  much 
as  is  required  to  accomplish  the  same  result  with  an  equal 
mass  of  iron.  It  is  not  surprising  then  that  land  surfaces 
heat  up  much  more  rapidly  than  water  surfaces.  How 


242 


WEATHER  AND  CLIMATE 


much  more  rapidly  cannot  be  stated  with  certainty,  because 
soils  differ  greatly  from  one  another.  The  darker  or  the 
coarser  the  soils,  the  more  rapidly  they  absorb  heat. 

There  is  another  very  important  difference  between  the 
heating  of  land  and  of  water  by  the  sun.  The  rays  of  the 

sun  penetrate  to  a 
greater  depth  in 
water  —  especially 
clear  water  —  than 
in  soil.  In  addition 
to  this,  the  water  is 
constantly  in  motion 
and  is  communicat- 
ing the  heat  from 
the  surface  to  the 
cooler  waters  below. 
Thus  the  summer's 
heat  affects  the  water 
many  feet  below  the 
surface.  This  makes 
a  lake  or  sea  a  veri- 
table storage  tank 
for  summer's  heat, 
yet  the  distribution 
of  heat  keeps  the 
surface  waters  rela- 
tively cool  in  sum- 
mer. 

The  land,  on  the  other  hand,  receives  all  of  the  sun's 
heat  upon  its  surface.  The  top  few  inches  of  soil  heat  up 
very  rapidly  every  summer's  day,  but  soil  immediately 
below  this  shallow  crust  never  becomes  very  warm,  and 


PALM  TREES  ON  TROPICAL  ISLAND  OF 
TAHITI 

There  is  almost  no  range  in  the  temperature 
of  this  island  throughout  the  year. 


SUMMER  AND  WINTER  EFFECTS  ALONG  A  SHORE    243 

does  not  show  appreciable  changes  of  temperature  except 
with  the  changing  seasons.  At  a  very  few  feet  below  the 
surface  the  soil  maintains  a  steady  temperature  summer  and 
winter. 

Surfaces  that  absorb  heat  rapidly  also  radiate  it  rapidly. 
A  large  percentage  of  the  heat  that  the  soil  has  absorbed 
during  the  day  is  given  out  to  the  atmosphere  at  night. 
But  the  water,  slowly  storing  heat  during  the  warm  months 
and  just  as  slowly  giving  it  out  during  the  cold  months, 
has  a  steadying  effect  upon  the  climate  of  the  land  adjoining. 
On  some  islands  of  the  sea,  the  range  of  temperature  through- 
out the  year  is  almost  imperceptible,  whereas  in  the  interior 
of  continents  the  average  temperature  of  some  of  the  summer 
months  is  more  than  a  hundred  degrees  higher  than  that 
of  some  of  the  winter  months. 

Day  and  Night  Effects  along  a  Shore.  —  In  the  summer, 
the  morning  sun  heats  the  soil  increasingly  until,  by  reflec- 
tion and  radiation  from  the  land  surface,  the  atmosphere 
above  it  is  highly  heated  and  expanded.  The  cooler  air 
flows  in  from  the  lake  or  sea  and  displaces  the  lighter  warm 
air.  If  the  sun  continues  to  shine,  this  landward  breeze 
persists  until  late  in  the  afternoon ;  but  its  effect  is  never 
felt  many  miles  inland.  At  night  when  the  rapidly  cooling 
soil  reaches  a  temperature  below  that  of  the  water,  the 
direction  of  the  breeze  is  reversed. 

Summer  and  Winter  Effects  along  a  Shore.  —  During 
the  summer  in  warm  climates,  water  is  heated  much  less 
rapidly  than  the  moist  air  above  it  and  so  it  absorbs  heat 
from  the  air  day  and  night.  This  cools  the  atmosphere, 
and  cooled  air  currents  from  above  the  water  temper  the  heat 
of  the  adjoining  land. 


244  WEATHER  AND   CLIMATE 

During  the  winter  the  water  gives  up  its  heat  more  slowly 
than  the  atmosphere.  As  it  gradually  yields  the  heat  it 
absorbed  during  the  summer,  the  air  above  it  is  warmed, 
and  currents  of  this  warmed  air  modify  the  temperature 
of  the  adjoining  land.  For  these  reasons  a  large  body  of 
water  slows  up  the  approach  of  warm  weather  in  spring 
and  of  frosty  weather  in  autumn. 

In  middle  latitudes  where  the  prevailing  winds  are  westerly, 
these  effects  are  naturally  much  more  marked  and  de- 
pendable on  the  east  shore  of  a  body  of  water  than  on  the 
west  shore.  In  many  places  on  the  east  shores  of  large 
lakes,  delicate  fruits  can  be  raised  because  the  steadying 
effect  of  these  bodies  of  water  prevents  early  "  warm  spells  " 
alternating  with  frosts  in  spring,  and  delays  the  autumn 
frosts  until  the  fruits  have  ripened.  The  tempering  effects 
of  warm  ocean  currents,  combined  with  prevailing  westerly 
winds,  account  for  the  mildness  of  climate  even  in  high  lati- 
tudes along  the  west  coasts  of  North  America  and  Europe, 
which  are  the  east  shores  respectively  of  the  Pacific  and 
Atlantic  oceans. 

SUMMARY 

The  earth's  atmosphere  acts  both  as  a  blanket  and  as  a 
sunshield  to  the  earth's  surface.  In  addition  to  this,  it  is 
the  circulatory  medium  of  the  earth,  without  which  there 
could  be  no  life. 

Winds  and  all  movements  of  air  are  caused  by  unequal 
heating  and  consequently  unequal  atmospheric  pressure  at 
different  places  on  the  earth's  surface.  The  prevailing 
directions  of  winds  are  also  affected  by  the  rotation  of  the 
earth.  Certain  winds  common  to  all  planets  are  called 
planetary  winds;  when  modified  by  certain  peculiarities  of 


SUMMARY  245 

the  earth  they  are  called  terrestrial  winds.  Because  of 
their  constancy  and  their  aid  to  traffic,  some  of  these  winds 
are  called  trade  winds. 

In  middle  latitudes  there  is  a  belt  of  irregular  winds  that 
have  a  prevailing  tendency  to  move  from  west  to  east.  This 
constant  eastward  drift  of  air  is  frequently  interrupted  by 
great  rotary  air  movements  having  a  diameter  of  from  500 
to  1000  miles.  These  are  called  cyclones  and  anti-cyclones. 
The  cyclone  is  an  area  of  storm,  and  the  anti-cyclone  is  an 
area  of  clear  sky.  These  eastward-moving  cyclones  are 
responsible  for  most  of  the  various  changes  in  our  weather. 
The  two  chief  factors  that  enter  into  the  forecasting  of 
weather  in  middle  latitudes  are  the  direction  of  movement 
and  the  rapidity  of  movement  of  cyclonic  areas. 

Brief  rainstorms  accompanied  by  lightning  are  called 
thunderstorms.  They  are  caused  by  local  updrafts  of  air 
over  hot,  moist  areas.  When  these  local  updrafts  become 
exceedingly  violent  and  of  small  diameter,  tornadoes  and 
waterspouts  result. 

'  When  moist  air  cools,  it  cannot  hold  as  much  moisture 
as  when  it  is  warm,  and  so  the  excess  falls  as  rain,  hail, 
snow,  or  sleet.  The  rainfall  varies  from  nothing  at  all  in 
some  places  to  over  fifty  feet  a  year  in  others.  In  the 
United  States  the  north  Pacific  slope  has  a  rainfall  of  about 
seventy  inches  a  year ;  the  south  Pacific  slope  about  fifteen 
inches;  the  eastern  slope  of  the  Rockies  is  very  dry;  and 
the  Mississippi  valley  and  the  country  to  the  east  of  it  have 
a  rainfall  of  from  thirty  to  sixty  inches. 

The  average  succession  of  weather  changes  throughout 
the  year  considered  for  a  long  period  of  years,  constitutes 
the  climate.  The  climate  of  any  section  depends  not  only 
on  latitude,  but  also  upon  altitude,  nearness  to  large  bodies 


246  WEATHER  AND   CLIMATE 

of  water,  kind  of  soil,  direction  of  prevailing  winds,  and 
many  other  causes. 

QUESTIONS 

How  does  the  atmosphere  affect  the  temperature  of  the  earth's 
surface? 

How  are  weather  maps  constructed  ? 

What  is  the  cause  of  winds? 

How  are  the  winds  of  the  earth  influenced  by  its  rotation? 

In  going  from  Boston  to  Cape  Horn  through  what  wind  belts 
would  a  sailing  vessel  pass  and  how  would  her  progress  be  affected 
by  the  winds  in  these  belts  ? 

Describe  the  wind  directions  and  cloud  conditions  before,  dur- 
ing, and  after  a  rainstorm  which  you  have  experienced. 

Describe  the  wind  and  cloud  conditions  of  a  thunderstorm. 

Upon  what  does  the  rainfall  of  a  place  largely  depend? 

How  is  the  rainfall  of  the  United  States  distributed  ? 

What  is  the  effect  of  mountains  upon  climate? 

How  do  large  bodies  of  water  affect  the  climate  along  their 
shores? 


CHAPTER  IX 

THE  EAKTH'S  OEUST 

Changes   in   the   Earth's   Condition.  —  Several   theories 
have  been  offered  concerning  the  original  conditions  of  the 


SPIRAL  NEBULA 

The  condition  of  one  of  the  faint  stars  as  revealed  by  the  tele- 
scope. It  is  millions  of  miles  in  extent.  Most  scientists 
believe  that  the  solar  system  was  in  such  a  nebular  state  as 
this  ages  ago. 

earth,  but  as  yet  no  one  of  them  has  been  fully  accepted. 
Almost  all  scientists  agree,  however,  that  the  matter  of 
the  earth  was  once  in  a  nebular,  or  gaseous,  state.  Uncounted 
ages  afterward  it  came  into  a  molten,  or  exceedingly  hot 
liquid,  condition ;  and  it  has  been  gradually  cooling  ever  since. 
247 


248  THE    EARTH'S   CRUST 

Whenever  borings  have  been  made  into  the  interior  of  the 
earth  it  has  been  found,  after  a  depth  has  been  reached  where 
there  is  no  effect  from  the  heat  of  the  sun,  that  the  tempera- 
ture rises  as  the  depth  increases.  From  this  gradual  in- 
crease in  temperature,  it  must  be  that  far  down  within  the 
earth  the  temperature  is  very  high.  The  pressure  within 
the  earth  is  so  great,  however,  that  rocks  at  great  depths 
are  probably  not  in  a  molten  condition.  If  the  earth  had 
a  liquid  interior,  the  attraction  of  the  other  bodies  of  the 
solar  system  would  cause  changes  in  its  shape ;  but  it  is  as 
rigid  as  steel. 

The  outside  cold  part  of  the  earth  is  called  its  crust.  How 
thick  this  is,  no  one  knows.  This  is  the  part  of  the  earth 
that  is  of  particular  interest  to  us,  for  it  is  the  only  part 
that  we  are  able  to  observe  and  study.  It  is  impossible 
for  us  to  conceive  the  eons  of  time  that  passed  while  the 
earth's  exterior  was  cooling  and  changing,  and  coming  into 
the  condition  in  which  we  know  it.  Geologists  think  in 
tens  and  hundreds  of  thousands  of  years.  The  mountains 
that  we  see  and  even  the  continents  we  live  on  are  the 
product  of  very  recent  changes,  as  geologists  measure  time, 
in  the  unimaginably  long  ages  that  reach  back  to  the  first 
gathering  together  of  matter  forming  the  earth. 

Experiment  80.  —  When  at  home  measure  the  greatest  and  least 
circumference  of  a  large,  smooth  apple  by  winding  a  string  around 
it  and  then  unwinding  and  measuring  the  length  of  the  string. 
Bake  the  apple.  Measure  its  circumferences  again.  Are  they 
greater  or  less  than  before  ?  Is  the  skin  of  the  apple  as  smooth  as 
it  was  before? 

There  is  every  reason  to  believe  that  the  interior  of  the 
earth  is  still  cooling  and  contracting.  Since  the  crust  is 
already  cooled,  it  has  ceased  to  contract.  Thus  as  the 


INTERCHANGE   OF   SEA  AND  LAND' 


249 


interior  shrinks,  the  crust  must  fold  up  in  order  still  to  rest 
upon  the  shrinking  interior.  The  wrinkling  of  the  skin  of 
the  baked  apple  as  the  interior  of  the  apple  cooled  gives 
a  faint  notion  of  what  has  been  happening  to  the  crust  of 
the  earth  through  the  ages.  The  cooling  of  the  earth  is  so 
slow  that  the  folding  usually  disturbs  the  surface  but  little 


FOLDED  STRATA 

at  a  time.  In  recent  hundreds  of  thousands  of  years,  there- 
fore, geological  changes  have  usually  taken  place  very 
gradually.  These  slow  changes  are  still  continuing,  and 
the  surface  of  the  earth  is  being  constantly  modified. 

Interchange  of  Sea  and  Land.  —  In  many  places  at 
considerable  distances  from  the  ocean,  sea  shells  have  been 
found  in  the  crust  of  the  earth.  Tree  trunks  are  sometimes 
found  at  considerable  depths  in  the  sea,  standing  with 


250 


THE   EARTH'S   CRUST 


TEMPLE  OF  JUPITER  NEAR  NAPLES 

Although  it  can  be  proved  that  this  coast  has  been  elevated  and  depressed 
several  times,  so  gradual  has  been  the  movement,  that  the  pillars  have 
not  been  overturned. 


OLD  SEA  BEACHES,  SAN  PEDRO,  CALIFORNIA 
Three  old  sea  beaches  can  be  distinctly  seen  on  the  promontory. 


INTERCHANGE  OF  SEA  AND  LAND 


251 


their  roots  penetrating  the  ocean  floor  just  as  they  stood 
on  dry  land.  It  can  be  proved  that  an  old  temple  near 
Naples,  Italy,  has  stood  above  and  then  in  the  sea  more 
than  once  since  it  was  built. 

Sometimes  old   sea  beaches  are  found  high  above  the 
shore   and   even  at   a   considerable  distance  inland.    Old 


OLD  ROCK  BEACH,  IMPERIAL  VALLEY,  CALIFORNIA 

This  is  many  miles  inland,  but  it  was  once  a  part  of  the  coast  of 
California. 

river  valleys  are  located  by  soundings  under  the  sea,  well 
out  from  the  present  mouths  of  rivers.  From  some  markings 
on  the  coast  of  northern  Sweden,  it  appears  that  the  coast 
has  risen  about  seven  feet  during  the  last  150  years.  Obser- 
vations along  the  coast  of  Massachusetts  give  reason  to 
believe  that  this  coast  is  sinking  very  slowly. 

Facts  like  these  show  that  the  seacoast  is  not  stable  but 
is  subject  to  upward  and  downward  movements,  some  of 
which  are  slight,  and  others  great. 


252  THE    EARTH'S   CRUST 

Characteristics  of  Land  Surfaces.  —  The  surface  of  the 
land  differs  from  that  of  the  sea  in  being  at  least  com- 
paratively immovable.  It  is  rough  and  irregular,  and  is 
composed  of  many  different  kinds  of  rocks  and  soils.  For 
the  larger  part  of  its  area  it  rises  above  the  level  of  the  sea, 
but  in  a  few  places  it  sinks  below,  as  in  the  Sal  ton  Sea, 
a  part  of  Imperial  Valley,  California,  and  near  the  Dead 
Sea  in  Palestine.  Its  surface  is  eroded  by  wind  and  water 
and  is  thus  constantly  but  slowly  changing  its  features. 

Materials  Composing  the  Land.  —  Experimental.  —  Obtain 
specimens  of  the  igneous  rocks,  lava,  obsidian,  basalt,  granite ;  of  the 
sedimentary  rocks,  sandstone,  fossiliferous  limestone,  conglom- 
erate, peat;  of  the  metamorphic  rocks,  gneiss,  schist,  marble, 
anthracite  coal.  Examine  these  carefully  with  the  eye  and  with 
a  lens,  noting  whether  they  have  a  uniform  composition  or  are 
made  up  of  different  particles.  Are  the  particles  composing  the 
rocks  crystalline?  Are  they  scattered  irregularly  or  arranged  in 
layers?  Test  with  a  file  or  knife-blade  the  hardness  of  the  rock  as 
a  whole  and  of  its  different  constituents.  Try  a  drop  of  hydro- 
chloric acid  on  the  different  rocks  to  see  whether  they  are 
affected  by  it.  Describe  in  a  general  way  the  characteristics  of 
each  specimen. 

The  composition  of  different  land  areas  varies  greatly. 
Many  different  kinds  of  rocks  are  often  found  crowded  to- 
gether, or  it  may  happen  that  the  same  kind  of  rock  covers 
a  large  area.  There  is  no  uniformity.  The  soil  on  top  of 
the  rock  is  also  variable.  In  some  places  it  contains  the 
minerals  which  are  in  the  rock  below  and  in  other  places 
its  composition  is  not  at  all  dependent  upon  the  bed  rock. 

The  great  variety  of  rocks  of  which  the  crust  of  the  earth 
is  composed  has  been  divided  into  three  great  groups  in 
accordance  with  the  manner  in  which  they  were  formed. 
These  groups  are  igneous,  sedimentary,  and  metamorphic. 


MATERIALS  COMPOSING  THE  LAND 


253 


GRANITE 

Igneous  rock  formed  deep  below  the 
surface  of  the  earth. 


The  igneous  rocks  are 
those  which  have  solidi- 
fied from  a  melted  con- 
dition. They  may  have 
solidified  deep  down 
within  the  crust,  or  on 
the  surface,  or  some- 
where between  the 
depths  and  the  surface. 
If  these  rocks  cooled 
slowly,  they  will  have  a 
crystalline  structure,  as 
in  granite,  and  if  very  rapidly,  a  glassy  structure,  as  in 
obsidian.  Their  structure  can  vary  anywhere  between 

these  two  extremes. 
A  common  dark 
colored  variety  of 
this  kind  of  rock  is 
called  basalt.  There 
are  many  varieties 
of  igneous  rocks,  but 
they  need  not  be 
considered  here. 

The  sedimentary 
rocks  are  those  that 
are  made  by  deposi- 
tion in  water.  When 
rocks  are  worn  away 
into  fragments  and 
these  fragments  are 

FOSSIL-BEARIXG  LIMESTONE  deposited     in    water 

A  sedimentary  rock  formed  from  sea  shells.         they  will,  under  cer- 


254 


THE   EARTH'S   CRUST 


tain  conditions,  harden  into  rocks.  The  shells  and  remains 
of  sea  animals  also  accumulate,  and  after  a  time  consolidate 
into  rock. 

About  four  fifths  of  the  land  surface  of  the  earth  is  com- 
posed of  sedimentary  rocks.  They  vary  greatly  in  color, 

durability,  and  use- 
fulness to  man. 

The  sandstones, 
which  are  composed 
of  little  grains  of 
sand  cemented  to- 
gether, are  used  for 
buildings  and  for 
many  other  pur- 
poses. The  lime- 
stones, which  are 
mostly  made  up  of 
the  remains  of  sea 
animals,  are  the 
source  of  our  lime 
and  are  also  used 
for  building  and  for 
other  purposes.  The 

shales  are  finely  stratified  mud  deposits  often  having  many 
layers  in  an  inch  of  thickness.  These  rocks  are  not  crystal- 
line. They  are  composed  of  fragments  of  other  rocks  or 
remains  of  plants  or  animals  and  usually  occur  in  layers 
or  strata. 

Bituminous  coal  is  sedimentary  rock,  formed  from  plants 
of  ages  ago  which  have  been  compressed  and  solidified  by 
enormous  and  long-continued  pressure. 

The    metamorphic    rocks    have    a    crystalline    structure, 


CONGLOMERATE 

A  sedimentary  rock  formed  from  old  gravel 
beds. 


STRUCTURE   OF  LAND  AREAS 


255 


GNEISS 
Probably  metamorphosed  granite. 


often  contain  well-formed 
crystals  embedded  in 
them  and  often  bands  of 
crystalline  substances  ex- 
tending through  them. 
These  rocks  are  modified 
forms  of  either  the  igne- 
ous or  sedimentary  rocks. 
The  original  igneous  or 
sedimentary  rocks  have 
been  subjected  to  forces, 
such  as  heat  and  pressure,  that  have  produced  physical  and 
sometimes  chemical  changes  in  them. 

Marble  is  crystallized  limestone,  and  gneiss  is  generally 
a  metamorphosed  granite.  Slate  and  mica-schist  are 
greatly  changed  clay  rocks,  and  anthracite  coal  is  a  metamor- 
phosed form  of  bituminous  coal.  The  rocks  of  this  group 
are  often  hard  to  distinguish  from  igneous  rocks. 

Structure  of  Land  Areas.  —  Not  only  do  the  land  areas 
differ  greatly  in  the  kind  of  rocks  of  which  they  are  com- 
posed, but  also  in  the  way  in  which  these  rocks  are  placed. 
Some  of  the  rocks  lie  nearly  in  the  condition  in  which  they 
were  originally  formed,  while  others  have  been  folded  and 
warped  and  twisted.  Vast  layers  of  rocks  have  been  worn 
away  by  the  forces  which  are  continually  wearing  away  and 
removing  the  rocks  at  the  surface  of  the  earth,  and  thus 
rocks  which  were  once  at  great  depths  below  the  surface 
have  been  exposed.  Even  granite  rocks  which  were  origi- 
nally formed  at  a  depth  of  thousands  of  feet  below  the  sur- 
face now  appear  at  the  surface  and  are  being  quarried  in 
many  places. 


256 


THE    EARTH'S   CRUST 


The  folding  and  warping  of  the  rock  layers,  as  shown  by 
the  picture  on  page  249,  has  brought  some  of  the  stratified 
beds  which  were  originally  horizontal  into  an  almost  verti- 
cal position,  so  that  we  now  find  at  the  surface  the  worn-off 
edges  of  these  beds.  The  different  kinds  of  rocks  and  the 

different  positions  in 
which  the  rock  layers 
are  presented  to  the 
forces  which  are  active 
in  wearing  them  away 
cause  great  variety  in 
the  forms  of  the  sur- 
face features. 


Continental  Shelf. 
—  Around  the  border 
of  the  continents  and 
of  those  islands  which 
are  near  the  conti- 
nents, there  extends, 


STRATIFIED  ROCK 

These  layers  have  remained  horizontal  as 
originally  formed. 


in  some  cases  to  a  distance  of  two  or  three  hundred  miles, 
a  gradually  deepening  ocean  floor.  This  gradually  deep- 
ening border  is  called  the  continental  shelf.  When  this 
floor  has  reached  the  depth  of  about  600  feet,  the  gradual 
slant  suddenly  changes  into  a  quick  descent  to  the  depths 
of  the  ocean,  two  or  three  miles. 

Upon  such  shelves  lie  the  great  continental  islands,  like 
the  British  Isles  and  the  East  Indies.  Continental  shelves 
furnish  the  great  fishing  banks  of  the  earth,  such  as  the 
Grand  Banks  of  Newfoundland  and  those  around  Iceland 
and  the  Lofoten  Islands,  where  fishermen  for  ages  have 
obtained  vast  supplies  of  fish.  There  is  no  equal  area  of 


CONTINENTAL  SHELF  257 

the  earth  where  the  life  is  so  varied  and  the  struggle  for 
existence  so  great  as  on  these  shallow  continental  borders. 
Jlere  the  mud  and  sand  brought  down  by  the  rivers  is 
spread  out  and  the  sedimentary  rocks  formed.  It  is  the 
elevation  of  this  shelf  which  has  formed  the  low-lying 
coastal  plains  which  border  many  of  the  continents.  There 
is  good  reason  to  believe  that  the  deep  floors  of  the  sea 
have  never  been  raised  into  dry  land,  and  that  the  vast 
extent  of  sedimentary  rocks  which  make  up  the  larger  por- 
tion of  the  land  has  almost  all  been  laid  down  in  regions 
which  were  at  the  time  continental  shelves. 

Coast  Effects  Resulting  from  Upward  Movement  of  the 
Earth's  Crust.  —  Experiment  82.  —  Tack  enough  sheet  lead  to  a 
very  rough  board  so  that  it  will  remain  submerged  when  placed  in 
water.  Place  the  board  in  a  shallow  dish  of  water,  lead  side  down. 
Taking  the  board  by  one  edge,  gradually  lift  this  edge  above  the 
water  surface.  What  kind  of  line  does  the  water  form  where  it 
meets  the  board?  In  what  way  would  this  line  be  changed  if  the 
board  were  smoother?  If  it  were  rougher?  If  the  edge-  of  the 
board  is  lifted  higher,  does  the  position  of  the  water  line  change? 
Does  its  form  materially  alter? 

Soundings  show  that  a  continental  shelf  has  a  compara- 
tively smooth  surface  and  a  gentle  slope.  If  the  shelf  is 
elevated,  a  strip  of  level  sea  bottom  is  added  to  the  dry 
land,  and  the  water  will  meet  this  new  shore  in  almost  a 
straight  line.  The  material  forming  the  shore,  both  above 
and  below  the  water  line,  will  be  easily  eroded  since  it  has 
been  recently  deposited  and  has  not  had  time  to  be  consoli- 
dated into  solid  rock. 

Waves  rolling  in  from  shore  will  strike  the  bottom  of  this 
gently  sloping  shelf  at  a  considerable  distance  off  shore. 
The  water  thus  loses  velocity,  and  deposits  much  of  the  solid 


258  THE    EARTH'S   CRUST 

material  it  is  carrying,  forming  a  sand  reef  at  some  distance 
from  the  shore. 

The  waterways  inclosed  between  sand  reefs  and  main- 
land are  often  of  sufficient  depth  to  form  protected  routes 
for  coastwise  traffic.  It  is  proposed  artificially  to  extend 
and  to  develop  certain  of  these  water  areas  along  the  eastern 
coast  of  the  United  States  so  as  to  form  a  protected  waterway 


INLAND  SEA  CAVE  AND  BEACH 
This  coast  has  been  recently  elevated. 

from  New  England  to  the  southern  ports.  At  present  the 
low,  almost  featureless  shore  of  this  region,  with  its  shifting 
sand  bars  and  capes,  makes  coastwise  navigation  dangerous, 
although  it  is  protected  by  many  lighthouses  and  life- 
saving  stations.  The  general  set  of  the  shore  currents  may 
singularly  modify  the  outlines  of  the  reefs,  as  is  shown  in  the 
formation  of  the  three  much  dreaded  capes  off  the  coast  of 
North  Carolina. 

Sand  hills,  "  dunes,"  form  upon  these  reefs,  building  them 


COASTAL  PLAINS 


259 


up  and  widening  them.  The  sand  reefs  along  the  southern 
Atlantic  and  Gulf  coasts  have  in  some  places  sufficient 
width  and  height  to  accommodate  large  settlements.  In 
time  the  sand  blowing  landward  from  these  reefs,  together 


COAST  NEAR  ATLANTIC  CITY 
Showing  marshes,  lagoons,  and  sand  reefs. 

with  the  silt  brought  by  the  streams  from  the  mainland,  may 
fill  up  the  water  area  (lagoon)  between  the  reef  and  the  main- 
land. The  filling  of  these  lagoons,  both  naturally  and  arti- 
ficially, has  greatly  increased  the  habitable  land  of  the  earth. 

Coastal  Plains.  —  A  coastal  plain  is  a  gradually  emerged 
sea  bottom,  and  so  has  shallow  water  extending  out  for  a 


260  THE    EARTH'S   CRUST 

considerable  distance  from  its  edge.  Along  the  shore  are 
marshes  and  lagoons  bordered  on  their  seaward  side  by  sand 
reefs,  where  the  winds  have  piled  up  the  sand  brought  in  by 
waves.  In  some  places  these  sand  reefs  are  so  situated  that 
they  are  valuable  for  habitation,  as  at  Atlantic  City,  New 
Jersey,  where  a  large  summer  resort  has  grown  up,  or  along 
the  coast  farther  south,  where  a  sparse  population  finds 
its  home  on  the  broader  reef. 

A  coastal  plain  increasing  in  width  toward  the  south 
extends  from  New  York  to  the  Gulf.  The  western  coast 
of  Europe  has  a  considerable  plain  of  this  kind.  The 
Netherlands  are  situated  on  land  which  has  been  either 
reclaimed  from  the  sea  naturally  in  recent  geological  time 
or  artificially  by  man  in  recent  historical  time.  In  the 
southern  part  this  reclamation  is  largely  due  to  the  sedi- 
ment brought  down  by  the  Rhine. 

In  the  western  part  of  the  United  States  the  coastal 
plain  is  not  as  well  developed  as  on  the  Atlantic  border. 
But  the  region  about  Los  Angeles  is  a  coastal  plain,  and 
almost  all  the  characteristics  of  the  broad  eastern  plain  can 
be  seen  in  traveling  from  the  ocean  to  the  coast  mountains. 

Coast  Effects  Due  to  Downward  Movement  of  the  Earth's 
Crust.  —  Experiment  83.  —  Cover  a  small  board  with  a  piece  of  thin 
oilcloth  which  has  been  most  irregularly  crumpled.  Take  the 
board  by  one  edge  and  inclining  it  slightly  gradually  submerge  it 
in  a  dish  of  water.  What  kind  of  a  line  does  the  water  form  where 
it  meets  the  oilcloth?  In  what  way  would  this  line  change  if  the 
oilcloth  were  more  crumpled?  If  it  were  less  crumpled?  If  the 
board  is  more  submerged,  does  the  position  of  the  water  line  change  ? 
Why  does  its  form  materially  alter? 

Along  a  coast  which  has  been  depressed,  the  shore  line 
has  moved  landward,  and  a  surface  rendered  irregular  by 


DEPRESSED    COASTS 


261 


erosion  is  lapped  by  the  inflowing  water.  All  the  irregu- 
larities which  lie  below  the  water  level  are  filled  with  water 
and  the  shore  line  bends  seaward  around  the  projecting 
elevations,  and  landward  into  the  gullies  and  valleys.  The 
tops  of  isolated  hills  now  stand  out  from  the  shore  as  islands. 
The  river  valleys  which  crossed  the  region  now  sub- 
merged reveal  themselves  only  to  the  sounding  line.  Their 


A  NORWAY  FIORD 
A  result  of  downward  movement  of  the  earth's  crust. 

landward  extensions  form  estuaries  up  which  the  tide  sweeps 
far  into  the  land.  The  unsubmerged  portions  of  these 
valleys  contain  fresh-water  streams,  the  size  of  which  seems 
insignificant  when  compared  to  the  size  of  the  estuary. 
Sheltered  coves  and  harbors  abound,  affording  protection 
to  all  kinds  of  craft  and  fitting  these  coasts  to  be  of  great 
commercial  importance. 

The  harvest  of  the  sea  replaces  what  might  have  been 


262 


THE   EARTH'S   CRUST 


the  harvest  of  the  land.  Since  the  distance  along  the  coast 
between  two  points  is  much  longer  than  the  straight  line 
distance  over  the  sea,  the  boat,  not  the  wagon,  becomes  the 
important  vehicle  of  travel. 

The  effect  of  a  submerged  and  eroded  coastal  plain  is 
seen  in  the  Delaware  and  Chesapeake  Bay  region.     Here 


A  SUBMERGED  COASTAL  PLAIN 

the  old  river  courses  have  been  submerged,  and  the  land  be- 
tween the  rivers  extends  into  the  ocean  in  narrow,  rather 
flat  strips  with  many  little  inlets  along  the  sides.  Easy 
water  communication  is  here  possible  to  a  considerable 


DEPRESSED    COASTS 


263 


distance  inland  and  to  almost  every  part  of  the  land  surface 
near  the  coast. 

When  the  country  was  first  settled,  these  water  courses 
were  most  advantageous  to  the  settlers,  as  the  produce  of 
the  farms  could  be  transported  to  sea-going  ships  with 
comparatively  little  difficulty,  much  more  easily  than  would 
have  been  the  case  if 
it  had  been  necessary 
to  carry  it  by  land. 
There  was  little  need 
of  building  roads,  as 
each  farmer  had  a 
protected  water  high- 
way to  his  door. 
Thus  a  part  of  this 
region  was  known  as 
"Tide-water  Vir- 
ginia." 

In  Norway  the 
deep  fiords  conduct 
the  sea  from  the  is- 
land-studded coast 
far  into  the  interior.  Their  sides  rise  steeply,  sometimes 
for  several  thousand  feet  from  the  water's  edge,  and 
descend  so  steeply  below  it  that  large  vessels  can  be  moored 
close  to  the  shore.  Generally  there  is  not  sufficient  level 
land  along  the  sides  of  the  fiord  for  building  roads.  The 
villages  are  usually  situated  where  a  side  stream  has  built 
a  little  delta,  or  at  the  heads  of  the  fiords  where  the  un- 
submerged  portion  of  the  valley  begins. 

It  was  such  a  coast  as  this  which  bred  the  ancient  North- 
men, to  whom  the  Sea  of   Darkness,  as   they  called  the 


A  NORWAY  FIORD 

Showing  large  vessels  anchored  in  the  deep 
water  close  to  the  shore. 


264  THE   EARTH'S   CRUST 

Atlantic,  was  terrorless.  While  less  favored  and  hardy 
sailors  were  dodging  from  bay  to  bay  along  the  shore  always 
in  sight  of  land,  they  were  pushing  boldly  west,  guided 


A  NORWAY  VILLAGE  AT  THE  HEAD  OF  A  FIORD 

only  by  the  beacons  of  the  sky,  and  discovering  Iceland, 
Greenland,  and  the  American  continent. 

Hills  and  Mountains.  —  Irregular  elevations  of  the 
earth's  surface  are  called  hills,  or  mountains  when  they  are 
of  considerable  height.  In  the  general  use  of  these  terms 
there  is  no  exact  line  of  separation.  Elevations  which  in 
mountain  regions  would  be  called  hills  would  in  a  flat  region 
be  called  mountains.  As  a  rule,  elevations  are  not  termed 
mountains  unless  they  are  at  least  2000  feet  high.  But  if 
the  general  elevation  of  the  country  is  great,  as  in  the  lofty 


STRUCTURE  OF  MOUNTAINS  265 

regions  of  the  Rockies,  an  elevation  to  be  termed  a  moun- 
tain must  rise  to  a  striking  height  above  the  generally 
elevated  surface,  which  is  itself  nearly  everywhere  more 
than  4000  feet  above  the  sea. 

Structure    of    Mountains.  —  Mountains    are   the   results 
of  deformations  in  the  earth's  crust,  due  to  causes  not 


LOFTY  MOUNTAINS 
The  high  Sierras. 

fully  understood.  The  crust  of  the  earth  has  been  folded, 
pushed  up,  crumpled  and  in  many  ways  distorted  so  that 
some  portions  have  been  elevated  to  great  heights  above 
sea  level. 

All  lofty  mountains  have  been  elevated  in  comparatively 
recent  geological  time,  but  this  of  course  means  millions 
of  years  ago.  If  mountains  now  lofty  were  geologically 
old,  they  would  long  ago  have  been  worn  down,  or  eroded, 
by  winds,  rain,  streams,  avalanches,  and  glaciers.  The 


266 


THE    EARTH'S   CRUST 


older  mountains  of  the  earth  are  all  comparatively  low,  not 
necessarily  because  they  were  never  elevated  as  high  as  the 
lofty  mountains  of  to-day,  but  because  their  greater  age  has 
longer  subjected  them  to  erosion  and  thus  reduced  their 
height. 

The  central  part  of  lofty  mountains  is  composed  of  igne- 
ous rocks,  but  on  the  sides  overlying  these,  sedimentary 
rocks  are  found.  The  Rockies,  the  Alps,  and  the  Himalaya 
Mountains  are  of  this  kind. 


THE  MATTERHORN 
A  famous  peak  in  the  Alps. 


Mountain  Peaks.  —  In  mountain  regions  the  features 
which  are  often  most  impressive  are  the  serrated  peaks 
which  rise  above  the  main  mass  of  the  mountains.  The 
shapes  of  these  peaks  vary  greatly  in  different  mountain 


MOUNTAIN  RANGES  267 

regions  and  tend  to  give  individuality  to  the  mountains. 
The  peaks  have  been  formed  by  erosion,  and  their  pecu- 
liarities are  due  to  the  different  kinds  and  positions  of  the 
rocks  from  which  they  have  been  carved. 

The  younger  mountains  which  have  not  long  been  sub- 
jected to  erosion  do  not  show  the  peak  and  ridge  structure. 
All  these  peaks  are  the  result,  not  only  of  original  uplift, 
but  of  subsequent  carving. 


THE  TETON  RANGE,  IDAHO,  U.  S.  A. 
Mountains  that  have  been  eroded  into  sharp  peaks. 

Mountain  Ranges.  —  As  a  rule  mountains  are  found 
in  ranges.  The  mountains  in  the  range  are  by  no  means 
all  the  same  elevation,  nor  is  the  range  necessarily  contin- 
uous, there  being  often  gaps  along  its  course.  Neither  were 
all  ranges  in  a  mountain  region  elevated  at  the  same  time. 
Those  which  make  up  the  mountain  region  of  the  western 
United  States  differ  much  in  the  time  of  their  elevation. 


268  THE   EARTH'S   CRUST 

Young  Plateaus.  —  Sometimes  large  areas  of  horizontal 
rock  are  elevated  high  above  the  sea,  forming  lofty  plains 
whose  surfaces  are  often  irregular,  owing  to  previous  erosion. 
Such  areas  are  called  plateaus.  The  descent  from  a  plateau 
to  the  lower  land  is  usually  steep.  Areas  of  this  kind, 
where  streams  are  present,  suffer  rapid  and  deep  erosion, 
since  the  grades  of  the  streams  are  steep  because  of  the 
elevation. 

If  there  is  not  much  rain  there  will  be  few  streams,  and 
these  will  have  deep  and  steep-sided  troughs.  Such  troughs 
render  the  area  very  difficult  to  cross.  The  valleys  are  too 
narrow  for  habitation  or  for  building  roads,  and  the  deep 
troughs  of  the  streams  are  too  wide  to  bridge.  Thus  the 
uplands  are  isolated. 

If  these  high  areas  are  in  a  warm  latitude,  they  are  desir- 
able for  habitation  on  account  of  their  cool  climate,  due  to 
the  elevation ;  but  if  in  temperate  latitudes,  their  bleak 
surfaces  are  too  cold. 

As  the  river  troughs  wear  back,  the  harder  rocks  stand 
out  like  huge  benches  winding  along  the  course  of  the  rivers. 
From  the  different  benches  slopes  formed  from  the  crum- 
bling of  the  softer  strata  slant  backward.  Thus  the  general 
outline  of  the  stream  sides  will  be  something  like  that  of  a 
flight  of  stairs  upon  which  a  carpet  has  been  loosely  laid. 

An  excellent  example  of  a  region  of  this  kind  which  has 
been  eroded  by  a  strong  river  gaining  its  water  from  a 
distant  region  is  that  of  the  Colorado  Canon  Plateau.  Here 
is  found  the  grandest  example  of  erosion  on  the  face  of 
the  earth.  The  rocks  are  of  various  colors ;  the  gorge  is 
nearly  a  mile  deep  and  in  places  some  fifteen  miles  in  width. 
Words  are  inadequate  to  express  the  grandeur  of  the  pan- 
orama spread  out  before  one  who  is  permitted  to  see  this 


YOUNG  PLATEAUS  269 

gigantic  exhibition  of  the  results  of  erosion.  Wonderful, 
grand,  sublime,  are  mere  sounds  which  lose  themselves  in 
the  ears  of  one  who  looks  out  upon  this  overpowering  dis- 
play of  Nature's  handiwork. 

The  region  is  very  dry,  and  the  river  receives  few  and 
short  branches  for  many  miles  of  its  course.     The  valley 


COLORADO  PLATEAU 
The  Colorado  River  has  cut  a  deep  cafion  through  this  high  plateau. 

is  widening  much  more  slowly  than  it  would  if  this  were 
a  land  of  considerable  rainfall,  and  as  yet  the  river  fills 
the  entire  bottom  of  the  gorge.  The  valley  is  in  the  early 
stages  of  its  development  and  the  erosive  forces  have  just 
begun  the  vast  work  of  wearing  down  the  region.  The  side 
streams  are  small  and  the  interstream  spaces  broad. 


270 


THE   EARTH'S   CRUST 


Dissected  Plateaus.  —  If  a  plateau  has  been  elevated 
for  considerable  time  in  a  region  of  abundant  rainfall,  the 
streams  extend  their  courses  in  networks,  thoroughly  dis- 
secting the  area  and  leaving  between  their  courses  only 
narrow  remnants  of  the  upland.  The  valleys  are  still 
deep,  but  the  intervening  uplands  are  of  small  extent. 
Traveling  over  the  region  in  any  direction  except  along 


THE  ENCHANTED  MESA,  NEW  MEXICO 
With  old  Indian  village  in  foreground. 

the  stream  courses  is  a  continual  process  of  climbing  out 
of  and  into  valleys. 

There  is  very  little  level  space  that  can  be  used  for  cul- 
tivation, and  on  account  of  the  steepness  of  the  slopes  it 
is  very  hard  to  build  roads.  The  river  valleys  are  so  narrow 
that  unless  the  roads  are  perched  high  up  on  the  sides, 
they  are  liable  to  be  swept  away  at  the  time  of  flood.  Farm- 
ing in  these  regions  is  very  discouraging  because  of  the  dim*- 


DISSECTED  PLATEAUS 


271 


culty  of  transporting  crops  and  of  finding  anything  but  a 
steep  side  hill  on  which  to'  grow  them. 

Railroads  can  get  through  only  by  following  the  princi- 
pal valleys,  and   here,  on  account  of  the  narrowness,  the 


A    BUTTE 

engineering  of  the  roads  is  difficult.  Unless  the  region  is  rich 
in  minerals,  it  can  support  only  a  small  population,  and  that 
will  of  necessity  be  poor.  If  the  forests  are  cut  off,  the  soil 
rapidly  washes  down  the  hillsides  and  leaves  naught  but  bare 
surfaces.  Regions  of  this  kind  are  found  in  the  Allegheny  and 
Cumberland  plateaus,  extending  from  New  York  to  Alabama. 


272 


THE   EARTH'S   CRUST 


Old  Plateaus. —  If  a  plateau  remains  elevated  for  a 
great  length  of  time,  the  rivers  are  able  to  widen  their  valleys 
and  wear  away  all  the  interstream  spaces,  except  where 
these  are  very  broad.  Thus  the  rivers  bring  the  whole 
surface  down  to  a  comparatively  low  level,  with  here  and 
there  a  remnant  which  has  not  been  worn  away,  but  which 
shows  in  its  steep  sides  the  edges  of  the  rock  layers  which 


AN  INDIAN  HOGAN 

formerly  spread  over  the  whole  region.  If  these  residual 
masses  are  large,  they  are  called  by  the  Spanish  name 
mesas,  meaning  tables,  and  if  small,  buttes,  from  the  French 
word  which  means  landmarks. 

Some  of  these  mesas  are  so  high  and  so  steep  that  it  is 
impossible  to  climb  them,  and  others  are  simply  low,  flat- 
topped  hills.  A  traveler  in  New  Mexico  and  Arizona 
will  see  many  of  these  mesas,  which,  like  the  lonely  Indian 


THE  GREAT  PLAINS  OF  THE  UNITED  STATES     273 

huts  or  hogans,  are  but  scattered  remnants  of  what  were 
formerly  widespread. 

On  old  plateaus  travel  is  easy.  There  are  no  deep  valleys, 
and  one  can  easily  pass  around  the  mesas,  which  only  add 
charm  to  what  would  otherwise  be  a  most  monotonous 


CLIFF  DWELLINGS,  ARIZONA 
A  protected  retreat  in  a  mesa. 

landscape.  When  these  mesas  are  high,  they  are  some- 
times occupied  by  a  few  Indian  tribes  who  have  fled  to 
them  for  protection,  as  the  medieval  barons  when  hard 
pressed  fled  to  their  isolated  castles. 

The  Great  Plains  of  the  United  States.  —  No  exact  dis- 
tinctions may  be  made  between  plains  and  plateaus.  Some 
surfaces  partake  of  the  nature  of  both.  West  of  the  Mis- 


274 


THE    EARTH'S   CRUST 


INDIAN  HIEROGLYPHICS  CUT  ON  THE 
STEEP  WALL  OF  A  MESA 


sissippi  River  the  open 
prairies  of  the  ngrth  and 
the  coastal  plain  of  the 
south  gradually  merge 
into  a  broad  extent  of 
territory  that  slopes  up- 
ward until  it  meets  the 
eastern  Rocky  Mountain 
plateau  five  or  six  thou- 
sand feet  above  sea 
level.  The  slope  of  this 
area  is  so  gradual  that 
the  change  of  elevation 
is  hardly  noticeable,  and 
so  it  is  called  the  Great 
Plains.  It  is  probable 
that  this  vast  expanse 


A  HIGH  DRY  PLAIN  IN  CENTRAL  NEVADA 


THE   GREAT  PLAINS  OF   THE  UNITED   STATES     275 

of  land  was  tilted  upward  when  the  crust  of  the  earth  was 
folded  upward  along  the  great  continental  divide. 

The  elevations  are  either  flat-topped  hills,  the  strata  of 
which  are  slightly  inclined  and  correspond  in  position  to 
those  found  in  the  plain  beneath,  or  they  are  masses  of  ig- 
neous material  which  appear  to  have  been  thrust  up  through 
the  rock  surrounding  them.  In  the  former  case  the  ele- 
vations are  simply  remnants  of  the  layers  of  rocks  which 
once  extended  over  the  country,  but  which  have  now  been 
eroded  away  over  the  larger  part  of  it;  in  the  latter  case 
they  are  the  igneous  masses  which  have  withstood  erosion. 


SUMMARY 

Almost  all  scientists  agree  that  the  matter  of  the  earth 
was  once  in  a  nebulous  state.  From  this  it  came  into  an 
exceedingly  hot  liquid  condition  and  then  into  a  solid  state. 
The  interior  of  the  earth  is  still  hot,  but  the  outside  part, 
or  crust,  is  cold.  As  the  interior  of  the  earth  is  still  cooling 
and  contracting,  the  crust  must  fold  in  order  still  to  rest 
on  the  shrinking  interior.  Thus  the  surface  of  the  earth 
has  been  slowly  changing  through  the  ages,  and  it  continues 
to  be  modified.  For  example,  the  sea  coast  is  not  stable 
but  is  subject  to  upward  and  downward  movements.  The 
surface  of  the  land  is  rough  and  irregular  and  different  land 
areas  vary  greatly  in  composition,  in  the  warping  and  fold- 
ing of  rock  layers  and  in  the  positions  of  these  layers.  The 
rocks  of  the  earth's  crust  are  divided  into  three  groups: 
igneous,  which  have  solidified  from  a  melted  condition; 
sedimentary,  which  are  made  by  deposition  in  water;  and 
metamorphic,  which  are  forms  of  igneous  or  sedimentary 
rocks  that  have  been  modified  by  natural  forces. 


276  THE    EARTH'S   CRUST 

The  ocean  floor  near  continents  slopes  off  gradually  until 
it  reaches  a  depth  of  about  600  feet,  when  it  suddenly  changes 
to  a  sheer  depth  of  two  or  three  miles.  This  gradually 
deepening  border  is  called  the  continental  shelf.  Upon 
such  shelves  lie  the  great  continental  islands  and  fishing 
banks.  The  upward  movement  of  these  continental  shelves 
gives  us  our  coastal  plains  and  has  greatly  increased  the 
habitable  land  of  the  earth.  The  depression  of  continental 
borders  has  given  us  our  estuaries,  deep  harbors,  and  con- 
veniently navigable  coasts. 

Mountains  are  the  result  of  folding,  pushing  up,  crumpling, 
and  other  distortions  of  the  earth's  crust  that  have  occurred 
during  ages  of  change.  Mountains  are  usually  found  in 
ranges  and  the  peaks  are  the  results  of  erosion.  Large 
areas  of  horizontal  rock  that  have  been  elevated  high  above 
the  sea  level  are  called  plateaus.  If  subject  to  great  erosion, 
plateaus  eventually  become  dissected  and  finally  worn  down 
to  a  comparatively  low  level,  with  only  occasional  mesas 
and  buttes  rising  here  and  there.  The  Great  Plains  are  a 
vast  sloping  surface  that  was  probably  tilted  upward  when 
the  crust  of  the  earth  was  folded  along  the  great  continental 
divide. 

QUESTIONS 

What  changes  have  taken  place  in  the  earth's  condition  ? 

To  what  great  classes  do  the  rocks  in  your  neighborhood  belong? 

For  what  would  you  look  if  endeavoring  to  determine  whether 
a  coast  had  been  elevated  or  depressed. 

What  advantages  does  an  elevated  coast  furnish  its  inhabitants  ? 
A  depressed  coast? 

To  what  is  the  height  of  mountains  due? 

Describe  the  characteristics  of  a  young  plateau. 

Why  do  not  dissected  plateaus  attract  a  dense  population? 

What  are  the  characteristic  features  of  an  old  plateau? 


CHAPTER  X 

PREPARATION    OF  THE  EAETH'S   SURFACE  FOE   PLANT 
LIFE 

Changes  in  the  Earth's  Surface. —  The  surface  of  the 
earth  is  constantly  changing.     In  fact  change  is  the  funda- 


A  RECENTLY  COOLED  LAVA  SURFACE  » 
A  surface  probably  somewhat  like  the  original  surface  of  the  earth. 

mental  law  of  life.     There  are  forces  constantly  building  up 
and  other  forces  just  as  steadily  tearing  down.  Sometimes 

277 


278     THE   EARTH'S  SURFACE  AND   PLANT   LIFE 

the  same  forces  are  doing  both.  It  is  impossible  to  tell 
which  set  of  forces  is  of  the  greatest  service  to  man;  be- 
cause without  either,  life  could  not  continue. 

It  is  believed  that  the  whole  surface  of  the  earth  originally 
hardened  from  a  molten  condition,  just  as  lava  from  a  volcano 
hardens  when  it  cools.  We  have  seen  that  the  waters  of  the 
sea  and  the  waters  that  run  over  the  land  are  wearing  away 


ROCK  SPLIT  BY  ROOTS  OF  TREE 

the  rocks,  grinding  them  together,  pulverizing  them,  and 
carrying  the  wreckage  to  other  places.  This  eroding  must 
have  begun  as  soon  as  the  earth's  crust  became  cool  enough 
for  the  waters  of  the  atmosphere  to  condense. 

It  is  necessary,  however,  to  take  into  account  not  only  the 
power  of  water  "to  wear  away  the  stones,"  but  also  its 
ability  to  hold  many  substances  in  solution  and  to  carry  them 
away  to  places  where  the  water  is  evaporated  and  the  dis- 


ROCK  WEATHERING  279 

solved  substances  deposited.  The  tremendous  power  of 
freezing  water,  the  weathering  power  of  the  atmosphere, 
the  wearing  and  transporting  power  of  the  wind,  the  scour- 
ing and  pulverizing  power  of  moving  ice,  and  the  never- 
ending  processes  of  growth  and  decay  have  also  greatly 
affected  the  earth's  surface. 

Experiment  84.  —  Allow  a  test  tube  filled  with  water  and  tightly 
corked  to  freeze.  What  happens?  If  the  temperature  of  the  air 
is  not  cold  enough,  place  the  test  tube  in  a  mixture  of  chopped  ice 
and  salt,  or  better,  chopped  ice  and  ammonium  chloride  (sal  am- 
moniac), and  allow  it  to  remain  for  some  time. 

Water  getting  into  the  cracks  of  rocks  and  expanding 
when  it  freezes  splits  them  apart  and  aids  much  in  their 
destruction.  Plant  roots  penetrate  into  the  crevices  of 
rocks  and  by  their  growth  split  off  pieces  of  the  rock.  Water, 
especially  when  it  has  passed  through  decaying  vegetable 
matter,  has  the  power  of  dissolving  some  rock  minerals. 
Certain  minerals  of  which  rocks  are  composed  change  when 
exposed  to  the  air  somewhat  as  iron  does  when  it  rusts. 

Rock  Weathering.  —  Experiment  86.  —  Weigh  carefully  a  piece 
of  dry  coarse  sandstone  or  coquina.  Allow  this  to  remain  in  water 
for  several  days.  Wipe  dry  and  weigh  again.  Why  has  there 
been  a  change  in  weight? 

Experiment  86.  —  Fill  a  test  tube  or  small  glass  dish  about  half 
full  of  limewater,  made  by  putting  about  2  ounces  of  quicklime  into 
a  pint  of  water.  Blow  from  the  mouth  through  a  glass  tube  into 
the  limewater.  There  is  formed  in  the  limewater  a  white  sub- 
stance which  chemists  tell  us  is  of  the  same  composition^  as  lime- 
stone. 

Experiment  87.  —  Continue  to  blow  from  the  mouth  for  a  con- 
siderable time  through  a  tube  into  a  dish  of  limewater.  The 
white  substance  disappears.  The  carbon  dioxide  of  your  breath 
dissolved  in  the  water,  forming  a  weak  acid,  and  caused  the  change. 


280    THE   EARTH'S  SURFACE  AND  PLANT   LIFE 

Now  if  we  heat  the  water,  thus  decomposing  the  acid  and  driving 
out  the  gas,  the  white  substance  again  appears. 

Oxygen,  carb9n  dioxide,  and  moisture  are  the  chief  weath- 
ering agents  of  the  atmosphere.  Rocks  which  are  exposed 
to  the  atmosphere,  especially  in  moist  climates,  undergo  de- 
composition. If  the  climate  is  warm  and  dry,  rocks  may 


ROCKS  WEATHERING  AND  FORMING  STEEP  SLOPES 

stand  for  hundreds  of  years  without  apparent  change,  whereas 
the  same  rock  in  another  locality,  where  the  weather  condi- 
tions are  different,  will  crumble  rapidly.  A  striking  example 
of  this  is  found  in  the  great  stone  obelisk,  called  Cleopatra's 
Needle,  which  was  brought  from  Egypt  to  Central  Park,  New 
York,  some  time  ago.  Although  it  had  stood  for  3000  years 
in  Egypt  without  losing  the  distinctness  of  the  carving  upon 


WIND   EROSION 


281 


it,  yet  in  the  moist  and  changeable  climate  of  New  York 
it  was  found  necessary  within  a  year  to  cover  its  surface  with 
a  preservative  substance. 

Not  only  do  different  climates  affect  differently  the 
wearing  away  of  rocks,  but  different  kinds  of  rocks  them- 
selves vary  much  in 
the  rate  at  which 
they  crumble.  It 
has  been  found  that 
while  marble  in- 
scriptions, in  a  large 
town  where  there  is 
much  coal  smoke 
and  considerable 
rain,  will  become 
illegible  in  fifty 
years,  that  after  a 
hundred  years  in- 
scriptions cut  in 
slate  are  sharp  and 
distinct. 

Where  the  tem- 
perature varies 
greatly  during  the 
day  the  expansion 
and  contraction  due  to  the  heating  and  cooling  sometimes 
cause  a  chipping  off  of  the  rock  surfaces. 


CLEOPATRA'S  NEEDLE,  CENTRAL  PARK, 
NEW  YORK 


Wind  Erosion.  —  The  artificial  sand  blast  is  in  common 
use.  In  it  a  stream  of  sand  is  driven  with  great  velocity 
upon  an  object  which  it  is  desired  to  etch.  In  nature  the 
same  kind  of  etching  is  done  by  the  wind-blown  sand. 


282     THE    EARTH'S   SURFACE   AND   PLANT    LIFE 


WIND-CUT  ROCKS,  GARDEN  OF  THE  GODS, 
COLORADO 

These  rocks  have  been  fantastically  cut  by 
wind-blown  sand. 


The  glasses  in  the 
windows  of  light- 
houses along  sandy 
coasts  are  sometimes 
so  etched  as  to  lose 
their  transparency. 
Rocks  exposed  to  the 
winds  are  carved  and 
polished ;  the  softer 
parts  are  worn  away 
more  rapidly  than 
the  harder  parts,  just 
as  in  all  other  forms 
of  erosion.  In  cer- 
tain regions  wThere 
the  prevailing  winds 

are  in  one  direction,  one  side  of  exposed  rocks  is  found  to 
be  polished,  while  the  other  sides  remain  rough. 

Wind  Burying  and  Exhuming.  —  In  exposed  sandy  regions 
where  there  are 
strong  winds,  ob- 
jects which  obstruct 
the  movement  of  the 
air  cause  deposition 
of  the  transported 
sand  just  as  obstruc- 
tions in  flowing 
water  cause  sedi- 
ment to  be  de- 
posited. And  just 
as  sand  bars  may  be 


deposited  by  a  river 


A  TREE  BEING  DUG  UP  BY  THE  WIND 


SAND  DUNES 


283 


and  then  carried  away  again,  owing  to  a  change  in  the 
condition  of  the  river's  load,  so  forests  and  houses  in  sandy 
regions  are  sometimes  buried,  to  be  uncovered  again 
perhaps  by  a  change  in  the  load  carried  by  the  wind. 

Sand  Dunes.  —  Sand-laden  wind  generally  deposits  its 
burden  in  mounds  and  ridges  called  sand  dunes  (page  258). 


A  FOREST  ON  CAPE  COD,  MASSACHUSETTS,  BEING  BURIED  IN 
WIND-BLOWN  SAND 

When  once  a  deposition  pile  begins,  it  acts  as  a  barrier  to 
the  wind  and  thus  causes  its  own  further  growth.  In  great 
deserts  where  the  wind  is  generally  from  one  direction,  these 
sand  dunes  sometimes  grow  to  a  height  of  several  hundred 
feet,  but  usually  they  are  not  more  than  20  or  30  feet  high. 
They  generally  have  a  gentle  slope  on  the  windward 
side  and  a  steep  slope  on  the  leeward  side.  The  sand  is 
continually  being  swept  up  the  windward  side  over  the 
crest,  thus  causing  the  dune  to  move  forward  in  the  direc- 
tion in  which  the  prevailing  wind  blows.  (Figure  92.) 


284     THE   EARTH'S   SURFACE   AND   PLANT   LIFE 

Almost  no  plant  life  can  find  lodgment  in  these  shifting 
sand  piles,  and  so  the  wind  continually  finds  loose  sand  on 
which  to  act,  and  a  dune  country  is  always  a  region  of 
shifting  sands.  As  the  dunes  move  in  the  direction  of 
the  prevailing  wind  they  sometimes  invade  a  fertile  coun- 
try, so  that  it  becomes  necessary  if  possible  to  find  a  way 
to  check  their  movement.  This  has  been  done  in  some 

places  by  planting  certain 
kinds  of  grasses  capable 
of  growing  in  the  sand 

^^^^_^^^_  and   thus  protecting  the 

FIGURE  92  sand    particles  from  the 

action  of  the  wind. 

Sand  dunes  are  found  along  almost  all  low  sandy  coasts, 
and  they  render  difficult  the  building  and  maintenance  of 
roads  and  railroads  to  many  beach  towns. 

Wind-borne  Soils.  —  Whenever  the  wind  blows  over 
dry  land,  particles  of  dust  and  sand  are  blown  away  and 
deposited  elsewhere.  The  interiors  of  our  houses  often 
become  covered  with  dust  blown  from  the  dry  streets.  Even 
on  ships  at  sea,  thousands  of  miles  from  land,  dust  has  been 
collected. 

In  volcanic  eruptions  great  quantities  of  dust  are  thrown 
into  the  air  and  spread  broadcast  over  the  earth.  On  the 
highest  and  most  remote  snow  fields  particles  of  this  dust 
have  been  found.  In  the  great  eruption  of  Krakatoa,  dust 
particles  made  the  complete  circuit  of  the  earth,  remaining 
in  the  air  and  causing  a  continuance  of  red  sunsets  for 
months. 

Sand  is  not  carried  so  far  as  dust,  but  at  times  of  strong 
wind  it  is  often  borne  for  long  distances.  Even  houses, 


SNOW  IN  WINTER  285 

trees,  and  stones  of  considerable  size  may  be  lifted  and 
moved  by  a  fierce  wind  storm.  The  wind-swept  detritus 
has  been  known  even  to  obstruct  and  modify  the  course  of 
streams.  Where  the  wind  blows  dust  constantly  in  one 
direction,  deposits  of  great  thickness  are  sometimes  made. 

In  Kansas  and  Nebraska  there  are  beds  of  volcanic  dust, 
reaching  in  some  places  to  a  thickness  of  more  than  a  score 
of  feet,  and  yet  there  are  no  known  volcanoes  either  past 
or  present  within  hundreds  of  miles.  In  China  there  is  a 
deposit  of  fine,  dustlike  material,  in  some  places  a  thousand 
feet  thick,  which  is  thought  by  some  to  be  wind  blown. 
This  forms  a  very  fertile  and  fine-textured  soil  and  supports 
a  great  population.  Many  of  the  inhabitants  of  the  region 
live  in  caves  dug  in  the  steep  banks  of  the  streams,  so  firm 
and  fine  textured  is  the  material.  Wind  deposits  of  this 
kind  are  called  loess  beds. 

Ice  as  a  Soil-builder.  —  The  agent  that  has  had  most  to 
do  with  preparing  the  soils  of  the  great  grain-bearing  regions 
of  Russia,  northern  Europe,  Canada,  and  the  United  States 
is  ice.  It  has  worn  down  and  pulverized  the  rocks  into 
soils,  has  mixed  and  transported  the  soils  from  regions 
farther  north,  and  has  laid  them  down  in  the  irregular 
surfaces  which  form  the  fertile  agricultural  fields  of  these 
regions  at  the  present  day.  Ice  has  been  the  master  soil- 
builder  of  much  of  the  tillable  land  of  the  world,  and  deserves 
careful  consideration. 

Snow  in  Winter.  —  When  the  temperature  of  the  air 
falls  below  the  freezing  point,  its  moisture  congeals  into 
little  flake-like  crystals  and  falls  as  snow.  Where  the 
cold  is  continuous  for  a  considerable  time,  the  snow  may 
accumulate  in  deep  layers  over  the  ground.  If  the  heat  of 


286     THE   EARTH'S   SURFACE   AND   PLANT   LIFE 

the  summer  is  not  sufficient  to  melt  all  the  snow  which 
falls  in  the  winter,  then  the  layers  of  snow  will  increase 
from  year  to  year. 

To  have  this  occur  the  temperature  for  the  whole  year 
need  not  be  below  the  freezing  point,  but  the  heat  of  the 
summer  must  not  be  sufficient  to  melt  all  the  snow  which 


anc 

s 


MOUNT  HOOD,  CASCADE  RANGE,  OREGON 
A  beautiful  old  volcanic  cone  which  is  continually  covered  with  snow. 

fell  in  the  colder  season.  Lofty  mountains,  even  in  the  trop- 
ics, have  their  upper  parts  snow-covered.  In  the  far  north 
ajid  the  far  south  the  line  of  perpetual  snow  falls  to  sea 
el,  inclosing  the  mighty  expanse  of  the  Arctic  and  the 
Antarctic  snow  fields. 


Glaciers.  —  Wherever  there  is  not  enough  heat  in  the 
warm  season  to  melt  the  snow  which  accumulates  during 


GLACIERS  287 

the  cold  season,  a  thick  covering  of  snow  and  ice  will  in 
time  be  formed.  The  ice  is  due  to  the  pressure  exerted 
on  the  lower  layers  by  the  weight  of  the  snow  above  and 
to  the  freezing  of  the  percolating  water  which  comes  from 
the  summer  melting  of  the  upper  snow  layers. 

Although  ice  in  small  pieces  is  brittle,  in  great  masses 
it  acts  somewhat  like  a  thick  and  viscid  liquid.  It  con- 
forms itself  to  the  surface  upon  which  it  lies,  and  under 


SNOW  FIELDS  AT  THE  HEAD  OF  A  GLACIER 

the  pull  of  gravity  or  pressure  from  an  accumulating  mass 
behind,  slowly  moves  forward,  resembling  in  some  ways 
thick  tar  creeping  down  an  incline  or  spreading  out  when 
heaped  into  a  pile.  Such  a  moving  mass  of  ice  is  called  a 
glacier.  The  exact  manner  of  glacial  movement,  however, 
is  not  fully  understood. 

In  mountain  regions  where  the  snow  holds  over  through 
the  summer,  the  wind-drifts  and  the  snow-slides  carry 
great  quantities  of  snow  into  the  upper  valleys,  until  ever 


288     THE   EARTH'S   SURFACE   AND   PLANT   LIFE 

accumulating  masses  of  snow  and  ice,  hundreds  of  feet 
thick,  are  formed.  The  ice  then  slowly  flows  down  a  val- 
ley till  a  point  is  reached  where  the  melting  at  the  end  is 
equal  to  the  forward  movement.  An  ice  stream  of  this 


GORNEB  GLACIER 
A  typical  Alpine  glacier. 

kind  is  called  a  valley  glacier  or  an  Alpine  glacier,  because 
first  studied  hi  the  Alps. 

Although  the  moving  ice  conforms  to  the  bed  over  which 
it  passes,  it  does  not  yield  itself  to  the  irregularities  as 
easily  as  does  water.  When  it  passes  through  a  narrows 
or  over  a  steep  and  rough  descent,  it  is  broken  into  long, 


GLACIERS  289 

deep  cracks  called  crevasses.  These  make  travel  along  glaciers 
sometimes  very  dangerous.  The  travelers  are  usually  tied 
together  with  ropes,  so  that  if  one  of  the  party  slips  into  a 
crevasse,  the  others  will  be  able  to  hold  him  up  and  pull 
him  out. 

A  glacier,  like  a  river,  is  found  to  flow  fastest  near  the 
middle  and  on  top,  and  slowest  at  the  bottom  and  on  the 


CREVASSES  IN  A  GLACIER 
Danger  points  in  travel  over  glaciers. 

sides.  The  rate  of  motion  in  the  Alpine  glaciers  varies 
generally  somewhere  between  50  fee^  and  one  third  of  a 
mile  in  a  year,  being  greatest  in  the  summer  and  least  in 
the  winter. 

Alpine  glaciers  are  found  not  only,  as  the  name  would 
indicate,  in  the  Alps,  but  also  in  Norway,  in  the  Himalayas, 


290     THE   EARTH'S   SURFACE   AND   PLANT    LIFE 


among  the  higher  mountains  in  the  western  United  States^ 
and  in  fact  wherever  the  snow  accumulates  in  the  mountain 

valleys     year     after 

i   T~ 

year. 

As  glaciers  creep 
down  the  valleys, 
dirt  and  rocks  .fall 
upon  their  edges 
from  the  upper  val- 
ley sides  and  are 
borne  along  upon 
the  ice.  If  two 
glaciers  unite  to  form 
a  larger  one,  the 
debris  upon  the  two 
sides  which  come 
together  forms  a 
layer  of  dirt  and 
rocks  along  the 
middle  of  the  larger 
glacier.  At  the  end 
of  the  glacier  this 
material  which  it  has 
borne  along  is  de- 
posited in  irregular 
piles,  of  rock  and 
dirt. 

The  accumulations 

of  debris  along  the  sides  are  called  lateral  moraines,  those 
in  the  middle,  medial  moraines,  and  those  at  the  end, 
terminal  moraines.  Great  bowlders  may  be  carried  along 
on  the  ice  for  long  distances  without  the  edges  being 


THE  FIESCH  GLACIER 
A  winding  "  river  "  of  ice,  bearing  a  medial 


GLACIERS 


291 


worn,  since  they  are  carried  bodily  and  not  rolled  as  in 
streams. 

On  the  under  surface  of,  the  glacier,  rocks  are  dragged 
along  firmly  frozen  into  the  ice.  The  weight  of  the  gla- 
cier above  presses  them  with  tremendous  force  upon  the  sur- 
face over  which  the  glacier  passes.  In  this  way  scratches 
or  grooves  are  made  in  the  bed  rock  underlying  the  gla- 
cier, as  well  as  upon  the  bowlders  themselves.  Scratches 


A  STONE  SCRATCHED  BY  A  GLACIER 

of  this  kind  are  called  glacial  scratches.  The  rubbing  of 
the  rocks  upon  each  other  wears  them  away  and  grinds 
them  into  fine  powder  called  glacial  flour,  which  gives  a 
milky  color  to  the  streams  flowing  from  glaciers: 

If  a  glacier  extends  over  a  region  where  the  surface  has 
been  weathered  into  soil,  this  fine  material  may  be  shoved 
along  under  the  ice  for  great  distances. 

Wherever  glaciers  are  easily  approached  they  form  a 
great  attraction  for  the  summer  tourist.  The  glistening 
white  snow  fields  circled  by  the  green  foliage  of  the  .lower 


292     THE   EARTH'S   SURFACE   AND   PLANT    LIFE 

slopes,  with  the  glaciers  descending  in  long,  white  arms  down 
the  valleys,  pouring  out  turbulent,  milky-colored  streams 
from  their  lower  ends,  and  here  and  there  covered  with 
bowlders  and  long,  dark  lines  of  medial  moraines,  form  a 
picture  which  once  seen  is  never  forgotten,  and  the  entice- 
ment of  which  lures  the  traveler  again  and  again  to  revisit 
the  fascinating  scene.  The  exhilaration  of  a  climb  over  the 


THE  DANA  GLACIER  IN  THF/  HIGH  SIERRAS 

pathless  ice  with  the  bright  summer  sun  shining  upon  it, 
the  bracing  air,  and  the  ever-changing  novelty  of  the  sur- 
roundings make  a  summer  among  the  glaciers  almost  like 
a  visit  to  a  land  of  enchantment. 

For  this  reason  Switzerland  has  become  the  summer 
playground  of  Europe  and  America.  There  the  tourist 
crop  is  the  best  crop  that  the  natives  raise,  and  the  scenery 
is  more  productive  than  the  soil. 

Norway,  with  the  additional  beauty  of  its  fiords,  is  fast 


GREENLAND  AND  THE  ANTARCTIC  ICE  FIELDS     293 

becoming  another  Mecca  of  the  tourist,  and  this  region, 
denuded  and  made  barren  by  the  ancient  glaciers,  is  now 
becoming  rich  and  prosperous  because  of  the  glacial  remnants 
still  left.  The  higlj  Sierras,  too,  are  each  year  enticing  greater 


A    VIEW    OF    THE    JUNGFRAU,    SWISS    ALPS 

Showing  the  snowy  mountains  and  verdant  valleys,  which  make 
Switzerland  the  delight  of  the  tourist. 

and  greater  numbers  of  travelers  to  enjoy  their  wonderful 
beauties  and  invigorating  climate. 

Greenland  and  the  Antarctic  Ice  Fields.  —  The  whole 
of  the  island  of  Greenland  is  covered  with  a  deep  sheet  of 
ice  except  a  narrow  border  along  a  portion  of  the  coast 
and  the  part  of  the  island  north  of  82°,  which  has  little 
precipitation.  The  extent  of  the  ice  sheet  is  nearly  equal 
to  the  combined  area  of  the  states  of  the  United  States  east 
of  the  Mississippi  and  north  of  the  Ohio.  The  depth  of  the 


294     THE   EARTH'S   SURFACE   AND   PLANT   LIFE 


ice  is  not  known,  but  probably  in  some  places  is  at  least 
several  thousand  feet.  Although  along  the  coast  moun- 
tains rising  from  5000  to  8000  feet  are  not  uncommon, 
yet  in  the  interior  the  thickness  of  the  ice  is  so  great  that 
no  peaks  rise  above  it. 

The  surface  of  the  inland  ice  is  a  smooth  snow  plain. 
Extending  from  this  ice  field  are  huge  glaciers  having  at 
their  ends  a  thickness  of  from  1000  to  2000  feet. 

In  the  Antarctic  region  an  area  vastly  greater  than 
Greenland  is  covered  with  ice  probably  of  a  greater  thick- 
ness. Although  little  is  known  about  this  ice  cap,  it  is 

thought  by  some  ex- 
plorers to  be  nearly 
as  large  as  Europe 
and  to  rest  partly  on 
an  Antarctic  conti- 
nent and  partly  on 
the  sea  bottom. 

Icebergs.  —  When 
a  glacier  extends  out 
into  the  sea,  the 
water  tends  to  float 

AN  ICEBERG  the    ICC.        If    it    CX- 

tends  out  into  deep 

enough  water,  the  buoyancy  of  the  water  will  be  sufficient 
to  crack  the  ice,  and  the  end  of  the  glacier  will  float  off  as 
an  iceberg.  Glacial  ice  is  about  eight  ninths  under  water 
when  it  floats. 

Icebergs  may  float  for  long  distances  before  they  melt. 
In  the  North  Atlantic  the  steamer  routes  are  changed  in 
the  summer  months  for  fear  of  running  into  floating  bergs. 


GLACIAL  PERIOD 


295 


Some  of  the  most  appalling  disasters  of  the  sea  have  been 
due  to  ships  colliding  with  icebergs. 

Glacial  Period.  —  Careful  examination  of  all  the  surface 
formations  over  large  areas  of  what  are  now  the  most  thickly 
populated  regions  of  North  America  and  Europe  has  led 
geologists  to  believe  that  at  a  former  period  in  the  earth's 
history,  perhaps  not  more  than  a  few  thousand  years  ago, 
the  northern  part 
of  both  continents 
was  covered  with  a 
thick  layer  of  ice. 
Evidences  of  this 
ancient  ice  covering 
are  seen  in  North 
America  as  far  south 
as  the  Ohio  River 
and  extending  over 
a  vast  region  which 
now  enjoys  a  tem- 
perate climate.  This 
mantle  of  ice  after 

several  advances  and  retreats  finally  disappeared,  leaving 
the  country  as  we  now  find  it. 

Although  the  border  to  which  the  ice  extended  and  many 
of  the  changes  which  the  ice  made  in  the  surface  of  the 
country  have  been  carefully  studied  and  mapped,  yet 
the  cause  of  this  extension  of  the  ice  and  the  exact  time 
at  which  it  occurred  have  not  yet  been  determined.  Many 
theories  have  been  brought  forward  to  account  for  it,  but 
none  of  them  explains  all  the  facts. 

That  the  ice  was  here  seems  to  be  sure,  but  exactly  when 


A  BOWLDER  BORNE  ALONG  ON  TOP  OF  \ 
GLACIER 

Notice  the  size  as  compared  with  the  umbrella. 


296     THE   EARTH'S   SURFACE   AND   PLANT   LIFE 


or  why  is  unknown.  This  period  when  the  ice  was  of  great 
extent  is  called  the  Glacial  Period.  Probably  during  the 
earth's  history  there  have  been  several  of  these  periods,  but 


AREA  IN  NORTH  AMERICA  COVERED  BY  THE  ICE  OF  THE  GLACIAL 
PERIOD 


to  the  last  is  due  the  great  change  wrought  upon  the  present 
surface  of  the  country  and  upon  plant  and  animal  life. 

The  greatest  ice  invasion  during  this  period  extended 
from  northern  Canada  across  New  England  into  the  sea, 


GLACIAL  FORMATIONS  297 

across  the  basins  of  the  Great  Lakes  and  the  upper 
Mississippi  valley  and  across  a  part  of  the  Missouri 
valley.  It  wrapped  in  its  icy  mantle  almost  the  entire 
region  between  the  Ohio  and  Missouri  rivers  and  the 
Atlantic  Ocean. 

Another  great  ice  invasion  spread  out  from  the  high- 
lands of  Scandinavia.  As  in  later  days  the  Norsemen,  so 
at  that  time  the  glacial  ice,  overspread  northern  Europe, 
carrying  Scandinavian  bowlders  across  the  Baltic  and  what 
is  now  the  basin  of  the  North  Sea,  forerunners  of  the  Scan- 
dinavian sword  which  in  later  ages  carried  devastation  to 
these  regions. 

Prehistoric  man  probably  saw  the  great  ice  mantle;  he 
may  even  have  been  driven  from  his  hunting  grounds  by 
its  slow  encroachment.  His  rude  stone  implements  are 
found  mingled  with  the  glacial  gravels.  But  like  the  spread- 
ing ice  he  has  left  no  record  from  which  the  time  or  cause  of 
the  Glacial  Period  can  be  determined. 

The  thickness  of  the  ice  over  these  central  areas  was  very 
great,  probably  approaching  a  mile.  The  pressure  on  the 
ground  below  must  have  been  tremendous  and  the  scouring 
and  erosive  effect  vast  indeed.  The  soil  which  previously 
covered  the  surface  was  swept  away  and  borne  toward  the 
ice  margin,  leaving  the  rocks  smoothed  and  bare. 

Glacial  Formations.  —  The  traces  left  by  these  ancient 
glaciers  are  unmistakable.  When  a  glacier  melts,  all  the 
material  which  it  has  moved  along  under  it  as  well  as  that 
which  it  has  carried  on  its  surface  or  frozen  in  its  mass  is 
deposited,  forming  what  is  called  ground  moraine.  This 
is  the  formation  which  constitutes  the  soil  of  many  of  our 
northern  states.  The  soil  throughout  the  glaciated  region 


298      THE   EARTH'S  SURFACE   AND   PLANT   LIFE 

is  not  of  the  same  composition  as  that  of  the  underlying 
rock ;  it  must  have  been  transported. 

Sometimes  the  end  of  a  glacier  remains  comparatively 
stationary  over  an  area  for  a  long  time,  owing  to  the  fact 
that  the  advance  of  the  ice  is  just  about  balanced  by  the 
melting.  In  this  case  the  morainic  material  which  has 
collected  on  the  top  of  the  glacier  is  deposited,  forming 
irregular  heaps  of  bowlders,  gravel,  and  sand,  with  inclosed 


BOWLDERS  AND  SAND  LEFT  BY  A  RETREATING  GLACIER 

hollows  between.  When  the  glacier  has  retreated,  ponds 
and  lakes  are  formed  in  the  depressions,  and  streams  wander 
about  in  the  low  places  between  the  morainic  heaps,  receiv- 
ing the  overflow  of  some  of  the  lakes  and  ponds.  The 
arrangement  of  the  streams  is  unsymmetrical  and  without 
order.  The  whole  surface  is  a  hodge-podge  of  glacially 
dumped  material  —  a  terminal  moraine  country.  It  was 
this  sort  of  country  that  made  the  East  Prussian  campaign 
of  the  World  War  so  difficult  for  both  Russians  and  Germans, 
and  rendered  the  final  defeat  of  the  Russians  so  disastrous. 


GLACIAL  FORMATIONS 


299 


A  VALLEY  IN  NORWAY  ROUNDED  OUT  BY  GLACIERS 

The  moisture  in  the  atmosphere  in  this  region  makes  it  necessary  to 
hang  the  hay  up  to  dry,  as  seen  in  this  picture. 

Where  a  glacier  has  little  load,  as  near  its  source,  the  bed 
rock  is  stripped  bare,  smoothed,  polished,  and  scratched  by 


300      THE   EARTH'S  SURFACE   AND  PLANT   LIFE 

the  material  which  the  ice  has  scraped  over  it  and  borne 
along.  Here  the  soil  that  is  left  when  the  ice  has  retreated 
is  very  thin.  Such  is  much  of  the  country  of  New  England 
and  of  eastern  Canada. 

The  valleys  through  which  glaciers  have  gone  are  left 
rounded  out  and  shaped  like  a  U. 


MARJELEN  LAKE 

Glacial  Lakes.  —  The  advancing  or  retreating  ice  may 
happen  to  make  a  barrier  to  the  escape  of  the  drainage, 
and  thus  may  form  a  lake  with  an  ice  dam  at  one  end. 
The  lake  will  continue  to  exist  only  so  long  as  the  ice  ob- 
structs the  drainage.  The  Marjelen  Lake  in  Switzerland 
is  a  well-known  example  of  this. 

Toward  the  close  of  the  Glacial  Period  a  vast  lake  of  this 
kind  was  formed  in  the  northern  part  of  the  United  States. 


PRAIRIES  OF  THE  UNITED  STATES  301 

It  extended  over  the  eastern  part  of  North  Dakota  and  about 
half  of  the  province  of  Manitoba.  The  slope  of  the  land  is 
here  toward  the  north.  As  the  ice  retreated  northward  it 
formed  a  barrier  to  the  drainage  and  dammed  back  a  great 
sheet  of  water  in  front  of  it.  When  the  ice  melted,  the  lake 
was  drained,  leaving  the  flat  fertile  plain  through  which  the 
Red  River  of  the  North  now  flows.  Glacial  lake  plains 
of  this  kind  form  fertile  areas  of  great  agricultural  value. 
The  North  Dakota-Manitoba  area  is  now  one  of  the  most 
productive  wheat  regions  in  the  world. 

Prairies  of  the  United  States.  —  North  of  the  Ohio 
River  and  extending  westward  beyond  the  Mississippi  is  a 
region  of  rolling  land  with  a  deep,  rich  soil.  .  Early  in  the 
last  century  it  began  to  be  rapidly  populated  on  account 
of  its  great  agricultural  advantages.  Owing  partly  to  the 
fineness  of  the  soil,  but  mostly  to  the  frequent  burning  over 
of  the  region  by  the  Indians,  the  area  was  destitute  of  trees 
except  in  some  places  along  the  river  courses. 

Thus  the  immigrant  did  not  need  to  go  to  the  trouble  and 
delay  of  clearing  the  forests  before  beginning  to  farm.  Culti- 
vation could  begin  in  earnest  with  the  first  spring,  and, 
as  a  rule,  rich  harvests  could  be  obtained.  The  soil  here 
is  transported  soil ;  it  is  deep  and  unlike  that  of  the  under- 
lying rock.  In  some  places  it  is  rather  stony  and  in  others 
very  fine  and  without  stones.  It  is  so  deep  that  the  under- 
lying local  rock  is  seen  only  in  deep  cuts. 

This  soil  was  probably  deposited  by  the  great  conti- 
nental glaciers  which  once  covered  the  region  and  was 
spread  out  either  by  the  action  of  the  slowly  moving  ice 
or  by  the  water  from  the  melting  ice.  This  water  flowed 
over  the  surface  in  shallow,  debris-laden  streams,  bearing 


302      THE   EARTH'S  SURFACE   AND   PLANT   LIFE 

their  silt  into  the  still  waters  of  transient  ice-dammed 
lakes.  Whatever  the  original  surface  of  the  region,  at 
present  it  is  an  irregularly  filled  plain  due  to  the  ancient 
ice  sheet.  As  the  soil  is  composed  of  pulverized  rock  not 
previously  exhausted  by  vegetable  growth,  it  is  strong  and 


ALFALFA  CUTTING  ON  THE  FERTILE  PRAIRIES 

enduring,  so  that  this  country  has,   since  its  settlement, 
been  noted  for  its  productivity. 

Soils  Produced  by  Decay.  —  All  the  agencies  we  have 
discussed  and  still  others  have  contributed  to  breaking  down 
the  rocky  crust  of  the  earth  into  soil,  thus  preparing  the  way 
for  plant  life.  The  very  plants  themselves  and  the  animal 
life  which  they  support  must  die  and  return  to  the  soil  from 
which  they  came.  If  it  were  not  for  this  the  earth  would 
eventually  be  encumbered  with  the  dead  forms  of  plants  and 
animals;  and  the  substances  of  which  these  bodies  are 
composed  would  eventually  be  exhausted  from  the  soil. 


CYCLES  OF  CHANGE  303 

Thus  even  decay  may  be  looked  upon  as  a  process  friendly 
to  man. 

Decay  is  a  very  complex  process.  It  is  produced  by  forms 
of  life  so  small  that  they  can  be  seen  only  with  a  microscope. 
There  is  good  reason  to  believe  that  there  are  forms  so 
small  that  even  the  most  powerful  microscopes  will  not  re- 
veal them.  The  most  important  of  these  minute  forms  of 
life  are  called  bacteria.  They  exist  in  uncountable  millions 
almost  everywhere.  Scientists  are  acquainted  with  over  1500 
different  kinds  of  bacteria,  and  each  kind  has  its  own  peculiar 
characteristics.  Molds  and  yeasts  are  other  low  forms  of  life 
that  help  in  the  processes  of  breaking  down,  or  disintegration. 

All  these  minute  forms  of  life  must  have  considerable 
moisture  and  some  of  them,  at  least,  must  have  free  oxygen 
in  order  to  thrive  and  to  accomplish  their  work.  Almost 
every  one  who  has  walked  through  the  woods  has  noticed 
how  much  more  rapidly  damp  wood  decays  than  dry  wood. 
It  is  to  keep  moisture  and  air  from  wood  that  we  paint  it, 
so  that  bacteria  may  not  have  in  it  living  quarters  favorable 
to  their  work  of  destruction. 

Cycles  of  Change.  —  Sometimes  areas  where  soils  have 
accumulated  for  centuries  and  centuries  have  been  grad- 
ually submerged  below  the  waters  of  the  sea.  There  these 
soils,  and  even  undecayed  plant  growths,  have  been  consoli- 
dated into  sedimentary  rocks.  Ages  afterward  these  areas 
have  again  emerged  and  the  whole  process  of  tearing  down 
has  begun  anew.  And  so  the.  cycles  of  building  up  and  tear- 
ing down  continue.  Sun,  water,  ice,  bacteria,  the  move- 
ments of  the  atmosphere,  and  the  slow  movements  of 
the  earth's  crust  are  constantly  working  in  league  with  one 
another  to  tear  down  what  many  of  the  same  agencies 
have  worked  steadily  to  build  up. 


304  SUMMARY 


SUMMARY 

The  surface  of  the  earth  is  constantly  changing;  in  fact, 
change  is  the  fundamental  law  of  life.  There  are  forces 
constantly  building  up,  and  other  forces  just  as  steadily 
tearing  down.  Among  those  forces  which  produce  change 
are  running  water,  with  its  power  to  erode  and  dissolve; 
freezing  water,  with  its  tremendous  expansion ;  the  moisture 
of  the  air;  the  gases  of  the  atmosphere;  heat;  and  the 
winds, 

But  the  agent  that  has  had  most  to  do  with  preparing  the 
soils  of  the  great  grain-bearing  regions  of  the  northern 
hemisphere  is  ice  in  the  form  of  glaciers.  Glaciers  have  their 
origin  in  upper  latitudes  or  altitudes,  where  the  snow  accumu- 
lates from  season  to  season  and  is  gradually  transformed  by 
pressure  into  ice.  This  may  spread  out  and  creep  down  the 
valleys  like  slow  flowing  rivers.  As  glaciers  creep  down  the 
valleys,  the  dirt  and  rocks  fall  upon  their  edges  from  the 
upper  valley  sides  and  are  borne  along  upon  the  ice.  These 
are  called  lateral  moraines.  If  two  glaciers  unite  to  form  a 
larger  one,  the  debris  upon  the  two  sides  which  come  to- 
gether forms  a  layer  of  dirt  and  rocks  which  is  called  a  medial 
moraine.  The  pressure  of  the  glacier  on  its  bed  also  wears 
away  the  rocks  and  pulverizes  them  into  soil.  When 
the  end  of. a  glacier  melts,  the  debris  that  is  deposited 
is  known  as  a  terminal  moraine. 

Almost  the  whole  of  the  island  of  Greenland  is  covered 
with  a  deep  sheet  of  ice.  The  depth  of  this  ice  sheet  is  not 
known,  but  probably  in  some  places  it  is  at  least  several 
thousand  feet.  In  the  antarctic  region  an  area  vastly 
greater  than  Greenland  is  covered  with  ice,  probably  of  a 
greater  thickness.  When  a  glacier  extends  out  into  deep 


QUESTIONS  305 

water,  especially  in  the  sea,  the  buoyancy  of  the  water  is 
sufficient  to  crack  the  ice,  and  the  end  of  the  glacier  floats 
off  as  an  iceberg. 

There  are  many  evidences  that  large  areas  of  what  are  now 
the  most  thickly  populated  regions  of  North  America  and 
Europe  were  once  covered  with  thick  layers  of  ice.  This 
mantle  of  ice  after  several  advances  and  retreats  finally  dis- 
appeared. The  period  of  the  last  of  these  several  advances 
of  glacial  ice  to  southerly  latitudes  is  called  the  glacial 
period.  These  ancient  glaciers  have  left  unmistakable 
traces.  They  scoured  out  depressions  in  the  earth,  some  of 
which  now  form  small  lakes  and  ponds.  They  pulverized 
the  rocks  in  their  course  and  transported  the  soil  thus  formed 
to  latitudes  where  it  now  serves  agricultural  purposes.  They 
changed  the  direction  of  flow  of  many  rivers  and  dammed 
back  great  sheets  of  water  into  lakes  which  disappeared 
when  the  glaciers  melted,  leaving  flat,  fertile  plains. 

The  very  plants  themselves  and  the  animal  life  which  they 
support  must  die  and  return  by  decay  to  the  soil  from  which 
they  came.  Thus  even  decay  must  be  looked  upon  as  a 
soil-forming  process  which  is  friendly  to  man.  Decay  is 
produced  by  bacteria  and  other  minute  forms  of  life  which 
must  have  considerable  moisture  in  order  to  thrive  and 
accomplish  their  work. 

Sun,  water,  ice,  bacteria,  the  movements  of  the  atmosphere, 
and  the  slow  movements  of  the  earth's  crust  are  constantly 
working  in  league  with  one  another  to  tear  down  what  many 
of  the  same  agencies  have  worked  steadily  to  build  up. 

QUESTIONS 

What  examples  of  rock  weathering  have  you  ever  seen? 
In  what  ways  has  wind  acted  as  a  soil  builder? 
In  what  ways  has  ice  acted  as  a  soil  builder? 


306      THE   EARTH'S  SURFACE  AND  PLANT  LIFE 

How  are  glaciers  formed  ?  How  have  they  modified  the  surface 
of  the  region  where  they  are  found? 

What  was  the  extent  of  the  North  American  ice  sheet  during  the 
Glacial  Period? 

How  has  the  Glacial  Period  affected  the  present  agricultural  and 
industrial  conditions  of  the  country  over  which  the  ice  spread? 

In  what  ways  does  the  process  of  decay  affect  the  soil  ? 


CHAPTER   XI 
MAN'S  USE  AND  CONSERVATION  OF  SOILS 

Importance  of  the  Soil.  —  The  World  War  has  awakened 
most  people  to  the  dignity  and,  importance  of  tilling  the 
soil.  For  once,  it  has  been  brought  home  to  us  that  we  are 
dependent  upon  the  nation's  farms  for  our  very  existence. 
From  the  soil,  either  directly  or  indirectly,  come  all  the 
necessaries  of  life,  our  food,  our  clothing,  and  most  of  the 
building-materials  and  furnishings  of  our  homes. 

Soil.  —  Experiment  88.  —  Into  a  16-oz.  bottle  nearly  full  of  water 
put  a  small  handful  of  sand,  and  into  another  bottle  about  the 
same  amount  of  pulverized  clay.  Shake  each  bottle  thoroughly 
and  allow  the  water  to  settle.  Which  settles  the  more  rapidly? 
Which  would  settle  first  if  washed  by  a  stream  whose  current  was 
gradually  checked  ? 

Wherever  the  inclination  is  not  too  steep,  we  find  the 
surface  of  the  bed  rocks  covered  for  varying  depths  with 
soil.  It  is  upon  and  in  this  that  plants  grow.  In  it  lies 
the  wealth  of  our  agricultural  communities.  On  examining 
this  soil,  it  will  be  found  that  in  some  places  it  grows  coarser 
and  coarser  the  farther  down  we  dig.  The  coarser  the  pieces 
become,  the  more  they  resemble  the  bed  rock,,  until  finally 
they  pass  by  imperceptible  stages  into  it.  This  kind  of 
soil  is  called  local  or  sedentary  soil. 

In  other  localities  the  coarseness  of  the  soil  does  not 
materially  change  as  we  dig  into  it,  but  suddenly  we  come 
307 


308    MAN'S   USE   AND   CONSERVATION   OF   SOILS 


upon  the  surface  of  the  bed  rock,  which  may  contain  few, 
if  any,  of  the  constituents  which  were  in  the  soil.     This 

soil,  which  in  no  way 
resembles  the  under- 
lying rock,  is  called 
transported  soil.  We 
have  already  learned 
how  most  of  it  reached 
its  present  position. 

The  first  kind  of 
soil  has  evidently  been 
formed  in  some  way 
from  the  rock  below, 
since  it  gradually 
shades  into  this  rock. 
This  kind  of  soil 
changes  with  the 
change  of  the  bed 
rock.  A  striking  il- 
lustration occurs  in 
Kentucky,  where  the 
rich  and  fertile  "Blue 
Grass "  region  is 
bounded  by  the  poor 
and  sandy  "  Barrens." 
The  one  is  underlaid 
by  limestone  and  the 
other  by  sandstone. 

The  soil  at  the  surface  is  usually  finer  than  the  soil  a 
foot  or  so  below  the  surface.  Sometimes  it  has  a  great 
deal  of  decayed  vegetable  matter  mixed  with  the  decom- 
posed rock  and  to  this  its  fertility  is  often  largely  due.  Some 


LOCAL  SOIL 

This  soil  has  been  weathered  from  the  under- 
lying rock. 


COMPOSITION  OF  SOILS  309 

soils  are  made  up  almost  entirely  of  decayed  vegetable  matter, 
peat,  and  muck.  The  underlying  coarser  and  lighter  colored 
soil,  which  contains  little  if  any  vegetable  matter,  is  usually 
called  the  subsoil. 

Composition  of  Soils.  — Experiment  89.  — Examine  under  a 
strong  magnifying  glass  samples  of  sand,  loam,  clay,  peat,  and  other 
kinds  of  soil.  Notice  the  differ- 
ent kinds  of  particles  composing 
the  different  soils  and  the  shapes 
of  these  particles. 

Experiment  90.  —  Put  a  hand- 
ful of  ordinary  loamy  soil  into  a 
fruit  jar  nearly  full  of  water  and 
allow  it  to  stand  for  a  day  or  two, 
shaking  occasionally.  At  the  end 
of  this  time  shake  very  thoroughly 
and  after  allowing  it  to  settle  for 
a  minute,  pour  off  the  muddy 
water  into  another  jar.  Allow 
this  to  stand  for  about  an  hour 
and  then  pour  off  the  roily  water 
and  evaporate  it  slowly,  being 
careful  not  to  burn  the  material 
left.  Examine  with  the  eye,  by  FIGURE  93 

rubbing  between  the  thumb  and 

fingers,  and  with  a  magnifying  glass,  the  three  substances  thus 
separated.  These  three  separates  will  be  composed  largely  of 
sand,  silt,  and  clay. 

If  a  compound  microscope  (Figure  93)  is  available,  mix  a  bit  of 
the  silt  and  of  the  clay  in  drops  of  water  and  put  these  drops  on 
glass  slides.  Examine  the  drops  under  the  low  power  of  the  micro- 
scope. Notice  the  little  black  particles  of  decayed  vegetable  mat- 
ter, also  the  little  bunches  of  particles  that  may  still  cling  together. 
Why  was  it  necessary  to  soak  the  soil  so  long?  Draw  the  shapes 
of  a  few  of  the  particles.  Describe  the  composition  of  the  soil  you 
have  examined. 


310    MAN'S  USE   AND   CONSERVATION   OF   SOILS 

If  we  examine  most  soils  with  a  microscope,  we  shall 
find  that  they  are  composed,  as  was  seen  in  Experiment  90, 
of  many  different  kinds  of  material.  Some  of  these  mate- 
rials dissolve  slowly  in  water  and  thus  furnish  food  for 
plants;  others  are  insoluble. 

In  different  soils  the  particles  vary  greatly  in  size  as 
well  as  in  composition.  In  gravel  the  particles  are  large 
and  in  a  gram's  weight  there  would  be  but  few ;  in  sands 


RELATIVE  SIZES  OF  SOIL  PARTICLES 
From  left  to  right :  clay,  silt,  sand,  gravel. 

there  are  many  more,  dependent  upon  the  fineness ;  in  silt 
particles  are  still  smaller ;  and  in  a  gram  of  clay  there  are 
several  billion  particles.  Agricultural  soils,  intermediate  be- 
tween sand  and  clay,  are  usually  called  loams.  There  are 
sandy  loams  and  clayey  loams,  with  many  intermediate 
varieties.  As  the  mineral  part  of  the  soil  is  derived  en- 
tirely from  the  rocks,  only  those  minerals  which  were  present 
in  the  underlying  rock  can  be  present  in  sedentary  soils, 
whereas  in  transported  soils  the  underlying  rock  has  had 
no  influence  upon  the  soil. 

The  minerals  composing  the   soil   must  furnish   certain 


WATER  FILM   OX   SOIL  PARTICLES  311 

substances  for  the  support  of  plant  life.  Many  of  these 
minerals  are  needed  in  such  small  quantities  that  most 
soils  have  an  abundance  of  them.  Nitrogen,  phosphorus, 
and  potassium  are  the  soil  elements  that  are  used  most 
freely  by  the  growing  plant. 

Plants  also  require  a  great  deal  of  water.  Yet  few  plants 
thrive  if  they  are  submerged  in  it,  or  even  if  their  roots  are 
submerged.  Air  is  also  necessary  to  the  growth  of  plants. 
Air  must  reach  not  only  the  part  of  the  plant  growing  above 
ground  but  the  underground  portion  as  well. 

But  if  a  soil  had  all  necessary  substances  for  plant  growth 
in  it,  it  would  still  lack  fertility  if  it  were  not  for  the  micro- 
scopic life  of  -the  soil.  Some  germs  increase  the  fertility 
of  the  soil  and  some  decrease  it.  If  those  which  increase 
fertility  are  to  thrive,  certain  conditions  must  be  main- 
tained. It  is  the  skill  of  the  agriculturist  in  maintaining 
and  increasing  these  favorable  conditions  which  largely  de- 
termines his  success  or  failure. 

Water  Film  on  Soil  Particles.  —  Experiment  91.  —  Take 
about  a  quart  of  soil  from  a  few  inches  below  the  surface  of  the 
ground  and  after  sifting  out  the  large  chunks,  put  it  in  a  sheet  iron 
pan  and  carefully  weigh  it  to  the  fraction  of  a  centigram.  Place  the 
pan  containing  the  soil  in  a  drying  oven  or  ordinary  oven,  the  tem- 
perature of  which  is  but  little  above  100°  C.  The  soil  should  be 
spread  out  as  thin  as  possible.  Allow  it  to  remain  in  the  oven  for 
some  time,  until  it  is  perfectly  dry  throughout.  Weigh  again.  The 
loss  of  weight  will  be  the  weight  of  water  contained  in  the  soil. 
As  there  was  no  free  water  in  the  soil  how  was  this  water  held? 
Dip  your  hand  into  water  and  notice  how  the  water  clings  to  it 
after  it  is  withdrawn.  Examine  with  the  eye  and  the  lens  several 
particles  of  the  original  soil  as  taken  from  the  ground  and  see  if 
there  is  a  water  film  on  each  of  these  as  there  was  on  the  wet  hand. 

Experiment  92.  —  Take  the  soil  that  has  been  dried  and  weighed 
in  the  previous  experiment  and  heat  it  throughout  to  a  red  heat 


312    MAN'S   USE   AND   CONSERVATION    OF   SOILS 

over  a  Bunsen  burner  or  in  a  very  hot  oven.  Weigh  again.  If 
there  is  still  a  loss  of  weight  this  must  be  due  to  the  burning  of  the 
organic  matter  —  rotten  twigs,  roots,  leaves,  etc.  — which  was  in 
the  soil.  Soils  differ  greatly  in  the  amount  of  water  they  contain 
and  in  the  amount  of  organic  substance  present, 

We  have  seen  from  Experiment  91  how  the  soil  takes 
up  water,  and  how  each  little  particle  has  a  film  of  water 
around  it.  Little  hairs  on  the  plant  roots  are  prepared 
to  take  up  these  little  films  of  water  which  surround  the 
soil  particles.  These  water  films  have  probably  dissolved 
a  minute  amount  of  material  from  the  soil  particles,  and 
this  material  enters  into  the  plant  and  can  be  used  for 
food. 

Experiment  93.  —  Compute  the  area  of  a  cubical  block  of  wood 
four  inches  on  a  side.  Cut  the  block  in  two.  Compute  the  com- 
bined area  of  the  two  pieces.  Cut  each  of  these  two  pieces  in  two. 
Compute  the  combined  area  of  the  four  pieces.  Cut  each  of  the 
four  pieces  in  two.  Compute  the  combined  area  of  the  eight  pieces. 
What  effect  does  dividing  the  block  into  smaller  and  smaller  pieces 
have  upon  the  total  surface  area?  Has  the  mass  or  volume  of 
the  wood  been  increased  ? 

We  found  in  Experiment  93  that  the  more  we  subdivided 
the  block  the  greater  was  the  combined  area  of  the  pieces. 
This  makes  clear  an  important  difference  between  coarse 
and  fine  soils.  The  smaller  the  particles  are  in  a  given  volume 
of  soil,  the  greater  is  the  total  surface  to  be  covered  by  film 
water.  Then  too,  the  smaller  the  particles,  the  more  readily 
are  they  dissolved  and  the  greater  is  the  amount  of  food 
within  reach  of  the  root  hairs  of  plants. 

Soil  air.  —  Experiment  94.  —  Fill  an  8-oz.  bottle  with  soil  taken 
from  a  few  inches  below  the  surface.  Fit  the  bottle  with  a  two- 
holed  rubber  stopper  having  the  long  neck  of  a  three  or  four-inch 
funnel  pushed  as  far  as  possible  through  one  hole  and  a  bent  de- 


FERTILE   SOILS'  313 

livery  tube  just  passing  through  the  other  hole.  See  that  there  is 
no  air  space  between  the  soil  and  the  stopper.  The  soil  in  the  bottle 
should  be  as  hard  packed  as  it  was  originally  in  the  ground.  If 
necessary,  push  a  wire  down  through  the  neck  of  the  funnel  so  as 
to  free  all  hard-packed  particles  of  soil  in  it. 

Connect  the  delivery  tube  with  a  bottle  full  of  water  standing 
inverted  on  the  shelf  of  a  pneumatic  trough.  Pour  water  into 
the  funnel  until  it  is  full,  and  keep 
it  full  during  the  rest  of  the  experi- 
ment. Allow  the  apparatus  thus 
arranged  (Figure  94)  to  stand  for 
some  hours.  Air  will  collect  in  the 
bottle  over  the  pneumatic  trough. 
Where  did  it  come  from  ?  When  the 
soil  in  the  bottle  has  become  entirely  „ 

saturated  with  water,  roughly  com- 
pare the  amount  of  air  collected  with  the  volume  of  the  bottle 
containing  the  soil.     What  part  of  this  soil's  volume  is  the  collected 
air? 

We  have  seen  by  this  experiment  that  soil  contains  air 
as  well  as  water.  Air  is  needed  if  plants  are  to  flourish ; 
and  it  is  necessary  that  soil  air  be  changed  frequently,  just 
as  it  is  necessary  that  air  in  living  rooms  be  changed  if 
people  are  to  flourish.  The  soil  must  be  ventilated.  Plant 
roots  must  have  air  to  breathe. 

Fertile  Soils.  —  Rock  disintegration  does  not  furnish 
all  the  complex  materials  needed  for  the  growth  of  agricul- 
tural plants.  Only  the  lower  orders  of  plants,  such  as 
lichens,  can  grow  on  soil  as  at  first  formed. 

A  fertile  soil  is  the  product  of  ages  of  plant  and  animal 
life,  labor,  and  decay.  One  of  the  most  important  plant- 
foods  that  is  furnished  by  these  means  is  nitrogen.  It  is 
an  element  that  enters  into  the  structure  of  every  living  thing. 
Practically  all  the  nitrogen  compounds  in  the  earth's  soil 


314    MAN'S   USE   AND   CONSERVATION   OF   SOILS 


have  been  put  there  either  by  the  decay  of  plant  and  animal 
matter  —  organic  matter  —  or  by  the  direct  efforts  of  cer- 
tain kinds  of  bacteria. 

Nitrogen  is  a  gas  that  constitutes  about  four  fifths  of  the 
atmosphere.  Yet  the  higher  forms  of  plant  and  animal 
life  can  no  more  use  the  free  nitrogen  of  the  atmosphere 


SOIL  IN  GOOD  TILTH 

than  a  human  being  can  digest  carbon.  The  nitrogen  must 
be  chemically  united  with  other  elements  into  compounds 
that  are  soluble  in  water  before  the  plant  can  make  use 
of  it  for  food.  Directly  or  indirectly,  plants  furnish  the 
entire  nitrogen  supply  of  animals.  Partially  decayed  organic 
matter  in  the  soil  is  called  humus. 

We  have  learned  that  decay  is  caused  by  minute  living 
things,  germs,  the  most  important  of  which  are  the  numerous 
kinds  of  bacteria.  The  soil  teems  with  this  germ  life. 
It  has  been  estimated  that  there  are  fifty  thousand 
germs  of  various  kinds  in  a  gram  of  fertile  soil.  Certain 
kinds  of  bacteria  work  the  humus  over  and  over,  each 


SOIL  FERTILIZERS  315 

kind  doing  a  different  work,  until  the  proper  nitrogen 
compounds  are  formed.  When  these  are  dissolved  in 
soil  water,  they  are  ready  to  be  taken  up  for  food  by  the 
plant. 

The  bacteria  of  decay  do  not  add  to  the  nitrogen  of  the  soil  ; 
they  simply  work  over  the  nitrogen  compounds  that  they 
encounter.  Without  their  activities,  the  growing  plant  would 
die  for  want  of  properly  prepared  food.  In  the  course  of 
decay,  various  acids  and  gases 
are  formed.  The  acids  help  to 
decompose  certain  minerals  into 
soluble  forms  that  the  plant 
can  use. 

If  the  acids  become  too  abun- 
dant, they  make  the  soil  "  sour," 
thus  preventing  the  growth  of 
needful  bacteria.  Such  soil  can 
be  readilv  "sweetened"  bv  the 

_  _  _  "        t  SOIL  BACTERIA 

addition  of  sufficient  lime.     It  is    . 

very  easy  to  test  whether  a  soil  is  sour  or  not,  by  placing 
a  piece  of  blue  litmus  paper  in  a  hole  in  the  ground  a  few 
inches  deep,  and  allowing  it  to  remain  there  for  several 
hours.  If  the  blue  litmus  paper  turns  red,  the  soil  is  sour. 
Wrhen  lime,  which  is  a  base,  is  mixed  with  sour  soil,  it 
unites  with  the  acids  of  the  soil  to  form  salts  that  are  not 
injurious  to  the  needed  bacteria. 

Soil  Fertilizers.  —  So  rapidly  do  the  growing  plants  use 
up  soluble  compounds  of  nitrogen  that  the  nitrogen  would 
soon  be  removed  from  most  soils  if  it  were  not  in  some  way 
replaced.  There  are  two  other  substances  that  are  much 
needed  by  plants  and  that  are. soon  exhausted  from  the  soil 


316    MAN'S  USE   AND   CONSERVATION   OF   SOILS 

by  the  growing  and  harvesting  of  crops.  These  are  phos- 
phorus and  potassium.  Wheat  crops,  for  example,  rapidly 
exhaust  soluble  phosphorus  compounds  from  the  soil ;  and 
generous  supplies  of  potassium  compounds  are  necessary 
for  the  successful  raising  of  cotton. 

Substances  that  contain  elements  needed  for  the  life  and 
growth  of  plants  are  called  fertilizers.     The  most  common 


SOUTHEBN  COTTON  FIELD 

fertilizers  are  manures.  They  contain  nitrogen,  potassium, 
and  phosphorus,  in  about  the  proportions  needed  for  the 
raising  of  ordinary  crops. 

Commercial  fertilizers  generally  contain  one  or  more  of 
the  three  elements  mentioned,  in  proportions  adapted  to 
the  needs  of  varying  crops.  Saltpeter  is  a  compound  rich 
in  nitrogen,  and  is  therefore  a  good  fertilizer.  The  most 
common  way  in  which  phosphorus  is  obtained  for  fertilizing 
is  in  the  form  of  phosphoric  acid.  Much  of  this  is  prepared 
at  stockyards  from  by-products,  formerly  wasted.  Phos- 


FERTILIZING  AGENTS  317 

phate  rocks,  which  are  derived  from  the  deposits  of 
bones  of  prehistoric  animals,  are  abundant  in  many 
places  and  furnish  tons  of  phosphorus  compounds  for 
fertilizing. 

Wood  ashes  enrich  soil  because  they  contain  potash. 
Up  to  the  beginning  of  the  recent  World  War,  the  great 
potash  beds  of  Germany  supplied  most  of  the  potash  used 
in  agriculture.  After  the  war  started  the  United  States 
began  making  efforts  to  locate  potash  beds  and  to  produce 
potassium  compounds  in  various  ways. 

In  October,  1918,  Secretary  Lane  of  the  United  States  De- 
partment of  the  Interior  announced  that  within  two  years 
the  United  States  would  be  independent  of  the  German 
supply.  Chemists  have  discovered  practical  processes  by 
which  to  produce  potash  from  the  brine  and  from  the  de- 
posits of  old  salt  lakes  in  certain  western  states.  They  have 
also  found  ways  of  extracting  potash  from  seaweeds,  which 
have  never  before  been  of  direct  service  to  man ;  from  minerals 
that  have  heretofore  been  considered  worthless;  from  the 
fumes  of  smelters  and  from  the  dust  of  cement  plants,  which 
have  hitherto  been  considered  not  only  useless  but  even 
injurious.  Thus  chemistry  turns  waste  into  wealth. 

Fertilizing  Agents.  —  Among  the  most  important  fer- 
tilizing agents  are  the  nitrogen-fixing  bacteria.  These  differ 
from  the  other  kinds  of  soil  bacteria  mentioned,  in  that  they 
are  able  to  take  nitrogen  directly  from  the  soil  air  and  to 
combine  it  into  compounds.  Farmers  know  that  if  a  field 
is  sowed  to  clover  or  to  soy-beans,  for  example,  it  becomes 
more  fertile.  This  is  owing  to  the  fact  that  the  nitrogen- 
fixing  bacteria  live  and  multiply  in  great  numbers  in  knots, 
or  nodules,  on  the  roots  of  these  plants.  When  the  clover 


318    MAN'S  USE   AND   CONSERVATION    OF   SOILS 


or  bean  crop  is  harvested,  the  roots  are  plowed  under  to 
enrich  the  soil. 

Animals  like  moles  and  gophers  plow  their  holes  through 
the  soil,  mixing  up  the  particles  and  making  the  soil  porous, 
so  that  the  water  can  readily  get  in  to  aid  in  breaking  up  and 

decomposing  the  soil 
particles.  These 
holes  also  provide 
openings  through 
which  plant  roots 
and  soil  organisms 
can  obtain  the  oxy- 
gen and  dissolved 
food  they  need. 
Ants  each  year  move 
vast  quantities  of 
fine  material  to  the 
surface,  and  in  some 
places  change  the 
surface  soil  in  a  few 
years. 

Angleworms,  the 
most  important  ani- 
mal soil  builders, 
channel  the  soil  with 
their  burrows,  thus 
providing  ready-made  openings  for  the  growing  roots  and 
by  increasing  the  porosity  of  the  soil  aid  in  its  ventilation 
and  drainage.  They  swallow  the  soil  as  they  make  their 
burrows,  in  order  to  get  the  decaying  vegetable  matter  for 
food,  and  they  grind  it  fine  as  it  passes  through  their 
bodies.  Every  year  they  bring  to  the  surface  great  quan- 


BACTERIAL  NODULES  ON  BEAN  ROOTS 


AGRICULTURAL  SOILS 


319 


titles  of  this  finely  ground  soil  mixed  with  the  undigested 
vegetable  matter.  Darwin  estimated  that  the  angleworms 
in  English  soil  deposited 
one  fifth  of  an  inch  of 
these  castings  each  year 
over  some  parts  of  the 
surface.  This  is  the 
finest  kind  of  fertilizer. 
It  is  a  conlmon  saying 
that  the  more  angle- 
worms the  better  the 
soil. 


This  soil  has  been  brought  from  below 
and  piled  up  by  the  ants. 


Agricultural  Soils.  — 
As  has  already  been 
shown,  soils  differ  greatly  in  fineness,  mineral  composition, 
and  waterholding  capacity.  They  also  differ  greatly  in  the 
amount  of  decayed  vegetable  material  or  humus  in  them. 

The  humus  is  a  most  im- 
portant soil  ingredient. 
It  not  only  furnishes 
plant  food,  but  it  also 
increases  the  capacity  of 
the  soil  for  holding  mois- 
ture and  prevents  the 
soil  particles  from  pack- 
ing together  too  closely. 
In  sandy  soils,  since 
there  is  usually  little  hu- 
mus, the  water  soon 
drains  out  and  plants  be- 


MOLEHILLS 


Showing  how  these  animals  burrow  up 
the  soil  and  make  it  porous. 


come  parched.  Such  soils 


320    MAN'S   USE   AND    CONSERVATION   OF   SOILS 

warm  up  quickly  in  the  spring  and  dry  out  rapidly  after 
long  wet  spells.  When  humus  and  plant  food  in  the  form 
of  manure  are  added,  these  soils  are  especially  adapted 
for  growing  early  crops  and  crops  that  do  not  require  a 
great  deal  of  moisture,  such  as  grapes.  The  "  Fresno 
Sand  "  of  California  and  the  sandy  coast  plains  of  the  east- 
ern United  States  are  soils  of  this  kind. 


LUMPY  SOIL, 
The  result  of  cultivating  at  the  wrong  time. 

In  clay  soil  the  particles  are  extremely  small,  as  are  also 
the  spaces  between  the  particles.  Water  is  therefore  taken 
up  very  slowly.  It  is,  however,  held  tenaciously.  Because 
so  much  heat  is  absorbed  in  raising  the  temperature  of  the 
soil  water  and  in  evaporating  the  water  that  slowly  rises 
to  the  surface,  clay  soils  are  cold. 

When  clays  become  wet,  they  are  very  sticky  and  cannot 
be  worked.  When  they  dry,  they  become  very  hard  and 
crack.  If  cultivated  at  the  wrong  time  they  break  into 
hard  lumps  and  render  further  cultivation  difficult.  The 


SOIL  WATER 


321 


adobe  soil  of  the  West  is  of  this  character.  If  the  soil  is 
nearly  pure  clay,  it  is  useless  for  farming.  If  sufficient 
sand  or  humus  can  be  added,  clay  soils  become  valuable, 
since  they  usually  contain  the  elements  needed  by  plants. 
A  soil  having  grains  about  midway  in  size  between  sand 
and  clay  is  called  a  s-ilt.  This  is  usually  a  most  fertile  soil. 
It  is  the  soil  of  the 
western  prairies  and 
the  great  grain-pro- 
ducing states  of  our 
country.  It  holds 
water  well,  contains 
an  abundance  of 
plant  food,  and  is 
easily  cultivated. 
Between  these  three 
types  —  sand,  silt, 
and  clay  —  there  are 
all  grades  of  soils, 
presenting  problems 
of  various  degrees. 
The  problem  of  the 
farmer,  however,  is 
to  maintain  a  soil 
which  holds  water 
but  is  well  drained, 

which  contains  the  elements  plants  need,  and  which  is 
mellow  enough  to  be  well  aired  and  to  let  the  plant  roots 
grow. 

Soil  Water.  —  Although  many  soils   contain    everything 
needful  for  the  production  of  agricultural  plants,  yet  the 


ADOBE  SOIL 

A  heavy  clay  soil,  very  fertile  but  hard  to 
cultivate. 


322    MAN'S  USE   AND   CONSERVATION    OF    SOILS 


rainfall  is  insufficient 
or  so  unevenly  dis- 
tributed that  these 
plants  are  unable  to 
grow.  This  is  true 
over  a  large  area  of 
the  United  States, 
and  the  same  condi- 
tions often  prevail 
over  the  usually  well- 
watered  part  of  the 
country  in  times  of 
drought.  The  ques- 
tion of  increasing 
MUD  CRACKS  the  water-holding 

Showing  the  way  clay  cracks  when  it  dries.         Capacity  and  of  pre- 
venting  the    loss   of 
water  by  evaporation  or  in  other  ways  is  a  very  important  one. 


PRAIRIE  SCENE 
Showing  modern  methods  of  harvesting  the  crop  from  fertile  silt  soil. 


SOIL  WATER 


323 


Experiment  96.  —  Weigh  out  equal  amounts  (about  100  g.  each) 
of  dried  gravel,  coarse  sand,  and  very  fine  sand.  Put  each  of  these 
into  a  four-inch  funnel  which  has  been  fitted  with  a  filter  paper. 
Pour  water  upon  each  until  all  that  can  be  absorbed  has  been 
absorbed.  Allow  each 
to  stand  until  water 
ceases  to  drop  from 
the  funnel.  Weigh 
again,  balancing  the 
weight  of  the  wet  filter 
paper  retainer  by  a 
similar  wet  filter  paper 
placed  on  the  weight 
side  of  the  scales. 
Which  of  these  sub- 
stances is  capable  of 
holding  the  most  water? 
Since  water  does  not 
penetrate  into  the 
grains  composing  these 
different  substances  the 
difference  in  water- 
holding  capacity  must 
be  due  to  the  different 
sizes  of  the  grains. 


If  we  dig  deep 
enough  into  almost 
any  soil  we  shall  find 
water.  Wells  show 
this.  Certain  trees 


ALFALFA  PLANT 
The  alfalfa  roots  go  deep  to  seek  water. 


and  plants  have  such  long  roots  that  they  can  reach  the 
underlying  water  and  flourish  where  other  plants  will  die. 
When  wet  lands  are  so  drained  by  tiling  that  the  plants 
can  send  their  long  roots  down  to  this  constant  water 
supply  or  water  table,  as  it  is  called,  they  stand  a  drought 


324    MAN'S   USE   AND   CONSERVATION    OF   SOILS 

much  better  than  plants  grown  on  undrained  land  where 
the  water  table  has  not  so  uniform  a  depth.  The  too  fre- 
quent surface  watering  of  plants  is  bad  for  them,  as  it  keeps 


RICE  SWAMP 
A  valuable  plant  growing  in  water. 

their  roots  so  near  the  surface  that  the  plants  are  unable  to 
withstand  slight  drought. 

Certain  kinds  of  plants  need  more  water  than  others. 
Water  lilies,  reeds,  rice,  and  other  plants  grow  with  their 
roots  submerged  in  water.  Other  plants,  such  as  the  cactus, 


SOIL  WATER 


325 


sagebrush,  and  mesquite,  can  grow  only  where  the  supply 
of  moisture  is  very  scant.  Most  cultivated  crops  cannot 
live  in  a  soil  that  holds  too  much  free  water ;  that  is,  water 
that  lies  between  the  particles  of  the  soil  instead  of  in  a  film 
around  them.  Too  much  free  water  excludes  the  air  from 
the  ground  and  the  plant  literally  drowns.  Even  where 
there  is  not  sufficient  free  water  to  drown  the  plant,  in- 
sufficient under-drainage  keeps  the  soil  cold  and  prevents 
the  injurious  substances  in  solution  from  being  washed  out 
of  the  soil.  This  explains  why  flowerpots  always  have  a 
drainage-hole  and  why  farmers  are  some- 
times compelled  to  tile  their  farms. 

Experiment  96. —  Place  small  glass  tubes 
of  several  different  bores  in  a  dish  of  colored 
water.  In  which  is  the  surface  of  the  water 
higher,  in  the  tubes  or  in  the  dish  ?  In  which 
tubes  is  it  the  higher,  those  of  large  or  small 
bore? 

Experiment  97.  —  Place  two  wide-mouth  4-oz.  bottles  side  by  side 
and  fill  one  partly  full  of  water.  Put  a  coarse  piece  of  cloth,  or 
better,  a  lamp  wick,  into  the  water  bottle  and  allow  the  other  end 
to  hang  over  into  the  empty  bottle.  (Figure  95.)  Allow  the  bot- 
tles to  stand  thus  for  an  hour. 
What  happens?  The  force  that 
causes  the  rising  of  water  up  tubes 
and  wicks  is  called  capillarity. 

Experiment  98.  —  Tie  pieces  of 
cloth  over  the  ends  of  four  lamp 
chimneys.  Fill  one  of  the  chimneys 
with  coarse  sand,  another  with  fine 
sand,  another  with  clay,  and  the 
fourth  with  a  deep  black  loam.  Stand  each  chimney  in  a  shallow  pan 
of  water.  (Figure  96.)  Allow  them  to  remain  for  a  week,  keeping 
water  in  the  pan  all  the  time.  Note  how  high  the  water  has  risen 
in  the  different  chimneys  at  the  end  of  an  hour ;  two  days  ;  a  week. 


FIGURE  95 


FIGURE  96 


326    MAN'S  USE   AND   CONSERVATION   OF   SOILS 


It  was  found  in  Experiment  91  that  each  little  particle 
of  soil  was  surrounded  by  a  film  of  water,  even  though  there 
was  apparently  no  water  in  the  soil.  This  film  will  be  re- 
placed, if  removed,  just  as  the  water  in  the  top  of  the  wick 
(Experiment  97)  was  replaced  by  water  flowing  up  the  wick. 

Roots  get  a  large 
part  of  their  water 
by  absorbing  the 
water  films  of  the 
soil  particles. 

Gravity  is  con- 
tinually pulling  the 
soil  water  deeper 
and  deeper  into  the 
ground.  This  deep 
soil  water  is  fre- 
quently diverted  to 
lower  ground  by 
impervious  layers  of 
soil  or  rock  and 
comes  to  the  surface 
as  springs,  or  it  may 
come  gradually  to 
the  surface  over  a  broad -area  a  long  distance  away  from 
where  it  fell  and  make  a  region,  otherwise  barren,  fertile  by 
subirrigating  it. 

Although  land  must  be  properly  drained,  the  loss  of  water 
by  drainage  may  in  some  cases  be  too  rapid.  It  is  often 
very  essential  to  stop  as  far  as  possible  downward  passage 
of  water,  or  seepage,  as  it  is  called.  The  water  in  seeping 
through  the  soil  dissolves  plant  food  and  if  allowed  to  drain 
off  would  decrease  the  fertility  of  the  soil.  Whatever  de- 


A  NATURAL  SPRING 
Coining  to  the  surface  between  rock  layers. 


EVAPORATION   OF   SOIL  WATER  327 

creases  the  porosity  of  the  soil  will  decrease  the  seepage  and 
thus  help  to  retain  the  plant  food.  This  may  be  done  by 
adding  humus,  and  sometimes,  where  the  soil  is  very  porous, 
by  rolling.  At  the  time  rain  is  likely  to  fall,  however,  the 
soil  must  be  kept  loose  and  mellow  so  that  the  water  can 
sink  into  it. 

Evaporation  is,  however,  the  cause  of   soil's  losing  the 
greatest  amount  of  water.     Soil  water  is  constantly  mov- 


AN  ARTESIAN  SPRING 
A  deep  water  layer  has  been  pierced  and  the  water  diverted  to  the  surface. 

ing  toward  the  surface  on  account  of  capillary  action,  and 
is  being  evaporated.  This  loss  by  evaporation  must  be 
counteracted,  if  in  arid  countries  or  during  dry  spells  agricul- 
tural plants  are  to  be  provided  with  sufficient  moisture. 

Experiment  99.  —  Fill  full  of  soil  four  tin  cans  having  small  holes 
punched  in  the  sides  and  bottom.  Water  each  with  the  same 
amount  of  water.  Cover  the  first  with  about  an  inch  of  grass  and 
the  second  with  about  an  inch  of  sawdust,  and  weigh  carefully. 
Weigh  the  third  and  fourth.  Record  the  weight  of  each. 
Thoroughly  stir  the  surface  of  the  third,  as  soon  as  it  is  dry  enough, 
about  an  inch  deep.  Keep  this  stirred.  Let  the  fourth  stand 
undisturbed.  Weigh  all  four  every  school  day  for  two  weeks. 


328    MAN'S   USE   AND    CONSERVATION    OF   SOILS 


Keep  a  record  of  the  loss  of  weight  of  each.  Why  have  they  lost 
weight?  How  do  the  grass,  the  sawdust,  and  stirring  of  the  earth 
affect  the  loss?  Suggest  ways  to  keep  soils  from  losing  their 
moisture. 

In  Experiment  99,  it  was  seen  that  if  a  layer  of  grass 
or  sawdust  was  put  on  the  top  of  the  soil,  the  moisture  did 


DRY  FARMING  IN  EGYPT 

not  evaporate  so  rapidly  as  it  did  when  the  soil  was  not 
covered.  The  grass  could  have  been  replaced  by  shav- 
ings, manure,  or  any  substance  which  would  protect  the 
ground  from  the  sun  and  wind.  Protections  of  this  kind 
are  called  mulches.  They  are  most  frequently  used  around 
trees,  vines,  and  shrubs.  It  is  impracticable  to  use  them 
extensively  on  growing  crops. 

It  was  also  found  that  soil  water  was  not  readily  evapo- 
rated where  the  top  of  the  soil  was  kept  stirred,  so  that 


SOIL  WATER 


329 


the  little  capillary  tubes  by  which  the  soil  water  reaches 
the  surface  were  broken  and  the  sunshine  and  air  were  kept 
from  the  under  part  of  the  soil  by  a  layer  of  finely  divided 
soil  mulch.  When  the 
surface  of  the  soil  is 
thoroughly  stirred  or 
cultivated  the  particles 
are  separated  so  far 
apart  that  the  water 
cannot  pass  from  one 
grain  to  another,  and  so 
is  retained  in  the  under 
layer  ready  for  the  plant 
roots.  Thorough  tillage 
of  agricultural  crops  is 
perhaps  the  best  way  to 
assure  the  plants  suffi- 
cient moisture  in  regions 
subject  to  droughts. 

In  some  parts  of  the 
arid  region  of  the  United 
States  dry  farming  is 
practiced.  The  soil  is 
deeply  plowed  and  the 
plow  often  followed  by 
a  bevel  wheel  roller  called 
a  soil  packer,  in  order  to  pack  the  under  soil  or  subsoil  so  that 
the  air  cannot  circulate  through  it  and  dry  out  the  upper 
soil.  The  surface  soil  is  then  most  thoroughly  cultivated 
so  as  to  make  as  perfect  a  soil  mulch  as  possible.  Thus, 
whatever  moisture  falls  is  kept  from  seeping  below  the  reach 
of  the  plant  roots  and  from  evaporating  from  the  surface. 


KAFFIR  CORN 
A  plant  suitable  for  dry  farming. 


330    MAN'S   USE   AND    CONSERVATION    OF   SOILS 

In  this  kind  of  farming  the  aim  is  to  use  more  than  one 
year's  moisture  in  growing  a  crop. 

Crops  are  usually  planted  only  every  other  year,  two 
years'  moisture  being  retained  for  one  crop.  The  soil  is, 
however,  kept  thoroughly  cultivated  all  the  time.  Of 
course  plants  requiring  the  least  amount  of  moisture  are 
best  adapted  to  dry  farming. 


IRRIGATION  IN  SQUARES 

Irrigation  is  the  most  efficient  means  of  raising  crops  in 
regions  of  insufficient  rainfall  or  of  droughts.  Water  is 
brought  to  the  land  from  distant  sources,  or  from  flowing 
artesian  wells,  or  is  pumped  from  wells  which  have  been 
sunk  to  an  -available  water  table.  In  this  way  water  can 
be  supplied  to  plants  whenever  needed.  Where  the  ground 
is  quite  level  it  is  often  flooded,  sometimes  in  larger  or  smaller 
squares,  with  little  ridges  separating  the  squares.  A  great 
deal  of  water  is  lost  in  this  way  by  evaporation. 


SOIL  WATER 


331 


Another  way  is  to  plow  furrows  eight  to  ten  inches  deep 
in  the  direction  of  the  surface  slope  and  run  the  water  into 
these  from  the  irrigation  ditch.  In  either  case  the  water 
is  allowed  to  soak  in  until  the  soil  is  thoroughly  wet.  The 
surface  is  then  cultivated  so  as  to  check  surface  evaporation. 
It  has  been  found  that  if  the  soil  in  certain  irrigation  regions 


IRRIGATION  IN  FURROWS 

does  not  have  adequate  under-drainage,  it  will  become  water- 
logged. Injurious  substances  from  the  soil  that  should  be 
carried  away  by  downward  seepage  and  drainage  are  dis- 
solved, carried  to  the  surface,  and  left  there  by  evaporation. 
In  such  cases,  artificial  under-drainage  has  proved  a  neces- 
sity. 

In  the  last  few  years  the  government  and  many  private 


332    MAN'S   USE   AND    CONSERVATION   OF   SOILS 

companies  have  spent  millions  of  dollars  in  putting  in  irriga- 
tion plants.  By  this  means  thousands  of  acres  of  land  which 
would  otherwise  have  been  valueless  for  agriculture  have 
been  made  exceedingly  productive. 

Alkali  Soils.  —  In  dry  regions  where  the  rainfall  all 
sinks  into  the  ground  and  after  remaining  for  a  time  rises 
to  the  surface  and  is  evaporated,  large  areas  are  found 
upon  which  almost  nothing  can  be  made  to  grow  even 


ALKALI  SOIL 
Few  plants  can  grow  here  because  of  the  excess  of  alkaline  salts. 

when  sufficient  water  is  provided.  Often  in  the  dry  sea- 
son white  or  brown  crusts  appear  scattered  over  the  sur- 
face in  large  patches.  The  white  crust  usually  tastes  like 
Epsom  salts  and  the  brown  like  sal  soda.  The  salts  form- 
ing these  patches  have  been  dissolved  out  of  the  soil  by  the 
soil  water  and  left  on  the  surface  when  it  evaporated. 

Such  substances  are  not  found  in  wet  regions  because 
they  are  carried  away  by  the  water  which  runs  into  the 
streams.  About  the  only  way  soil  of  this  kind  can  be  treated 
to  make  it  productive  is  to  irrigate  and  drain  it,  thus  washing 
the  salts  out  of  the  soil.  This  is  just  what  is  done  by  nature 


SOIL  AND  MAN 


333 


in  well-watered  re- 
gions. Sometimes  if 
there  is  not  much 
alkali,  deep  plowing 
or  the  planting  and 
removal  of  certain 
plants  such  as  sugar 
beets,  which  are  ca- 
pable of  growing  in 
such  soils,  will 
sweeten  it. 

Soil  and  Man.  — 
Although    nature 
through       countless 
ages  has  been  preparing  the  soil,  and  generation  after  genera- 
tion of  plants  and  animals  has  been  contributing  to  its 


RECLAIMING  ALKALI  SOIL  IN  THE  SAHARA 


ROMAN  PLOWING 
Showing  primitive  methods. 


334    MAN'S  USE   AND   CONSERVATION   OF   SOILS 

fertility,  yet  it  will  not  continue  profitably  to  produce 
agricultural  crops  unless  carefully  handled  by  man.  The 
materials  taken  from  it  must  be  replaced  by  fertilizers.  It 
must  also  be  thoroughly  tilled  in  order  (1)  to  keep  in  the 
moisture,  (2)  to  prepare  a  mellow  place  where  the  roots  of 
the  plants  may  spread,  (3)  to  provide  air  and  water  and 


LABOR-SAVING  MACHINERY 

Two  men  with  a  tractor  operate  two  binders  and  two  shockers.  The 
shocker  is  a  new  invention  which  receives  the  bundles  of  wheat,  auto- 
matically assembles  from  8  to  11  of  them  into  a  shock,  and  deposits 
the  shock  right  side  up.  Each  shocker  saves  the  labor  of  at  least  two 
men. 

humus  needed  by  the  bacteria  which  build  up  the  solu- 
ble nitrogen  compounds,  and  (4)  to  kill  the  weeds  which 
would  use  the  space  and  plant  foods  needed  by  the  grow- 
ing crops  and  would  choke  them  out.  Proper  tillage  prob- 
ably has  more  to  do  with  thrifty  and  productive  farm- 
ing than  any  other  one  thing.  By  careful  tillage  much 
expense  for  fertilizers  can  be  saved  and  the  value  of  the 
crop  produced  greatly  increased. 


VALUE   OF  SOILS  335 

Value  of  Soils.  —  Many  different  factors  enter  into 
the  determination  of  the  value  of  a  soil.  Soils  which  in 
one  locality  would  be  of  great  value  are  almost  valueless  in 
other  localities.  Light  sandy  soil  far  from  a  market,  un- 
less transportation  facilities  are  exceptionally  good,  is 
almost  worthless,  while  the  same  soil  near  a  city  where 


GOOD  SOIL,  A  TRUCK  FARM 

fertilizers  can  be  easily  procured  and  where  early  vege- 
tables find  a  ready  market  is  of  great  value. 

Different  soils  are  adapted  to  different  crops,  and  where 
a  soil,  although  not  good  for  many  crops,  is  adapted  for 
raising  a  crop  which  in  its  locality  is  valuable,  the  soil  is 
called  good.  Thus  the  soil  in  many  parts  of  Florida, 
although  unsuited  for  raising  most  crops,  is  suited  for 
orange  trees  and  early  vegetables,  and  so  is  a  good 
soil.  The  stony  soil  in  certain  of  the  orange  regions 
of  California  would  be  an  exceedingly  poor  soil  for  most 
crops,  but  it  is  good  for  oranges  and  therefore  it  is  most 
valuable. 


336    MAN'S   USE   AND   CONSERVATION   OF   SOILS 

Reclamation  of  Arid  Lands  and  Low  Lands. —  Four 
thousand  years  ago  the  Assyrians  made  a  veritable  garden 
of  the  Tigris  and  Euphrates  valleys  by  dredging  lakes  for 
the  conservation  of  river  flood  waters  and  canals  for  distri- 
bution. Tanks,  reservoirs,  and  irrigation  canals  were  in  exist- 
ence in  India  centuries  before  Christ.  There  are  evidences 


EAST  END  OF  THE  ASSUAN  DAM  ACROSS  THE  NILE 
The  greatest  irrigation  dam  in  the  world. 

that  a  prehistoric  race  had  extensive  irrigation  works  cen- 
turies ago  in  New  Mexico  and  Arizona. 

Modern  methods  of  irrigation  make  it  possible  to  reclaim 
large  tracts  of  land  that  must  have  remained  waste  lands  in 
ancient  days.  The  building  of  great  dams,  the  construc- 
tion of  permanent  ditches,  and  even  the  boring  of  water 
courses  through  the  sides  of  great  mountains,  are  among 
the  great  tasks  performed  by  the  United  States  Govern- 
ment and  by  private  companies  in  reclaiming  large  areas 
of  land  in  arid  sections  of  the  West. 


RESULTS  OF  A  SUDDEN  FLOOD 
Soil  and  even  buildings  have  been  swept  away. 


A  CYPRESS  SWAMP  IN  LOUISIANA  BEFORE  DRAINAGE 

A  floating  dredge  is  used  to  cut  a  canal  around  the  area   to  be  reclaimed. 
The  earth  excavated  from  the  canal  is  piled  into  an  embankment  inclos- 
ing the  tract.     In  this  tract  a  network  of  drainage  canals  and  ditches  is 
dredged  from  which  the  surface  water  is  pumped  out. 
337 


338    MAN'S   USE   AND   CONSERVATION    OF   SOILS 

But  there  are  other  sections  where  by  another  sort  of  work 
millions  of  acres  of  exceptionally  fertile  soil  may  be  re- 
claimed. Rich  flood  plains  must  be  protected  against 
periodic  overflows  that  often  ruin  crops  and  sometimes 
ruin  even  the  soil  itself.  The  building  of  systems  of  levees 


CYPRESS  SWAMP  RECLAIMED 


This  is  the  same  section  that  was  shown  in  the  preceding  illustration,  after 
the  land  had  been  drained,  cleared,  and  staked  out  for  cultivation. 

would  prevent  this,  and  the  establishment  of  flood  basins 
to  catch  the  overflows  from  the  rivers  would  furnish  farmers 
in  these  sections  with  water  for  irrigation  during  the  dry 
months  that  often  succeed  floods.  The  United  States  may 
well  profit  by  the  examples  of  ancient  peoples  in  reclaiming 
such  lowlands.  Undrained  areas  of  the  Great  Lakes  region 
and  of  the  coastal  plains  may  also  be  reclaimed,  as  Holland 


FORESTRY 


339 


and  Belgium  have  reclaimed  so  much  of  the  surface  of  those 
fertile  countries. 


Forestry.  —  When  rain  drops  upon  the  foliage  of  trees, 
its  force  is  broken  and  it  falls  to  the  ground  in  fine  spray. 
If  the  ground  beneath  is  carpeted  with  leaves  and  humus, 
the  soil  is  further  protected  from  erosion.  The  water  readily 


BAD  LANDS  OF  DAKOTA 
Running  water  has  so  dissected  this  land  as  to  render  it  valueless. 

soaks  into  the  soil  made  spongy  by  leaves  and  roots.  When 
the  rain  is  over,  evaporation  does  not  take  place  rapidly 
because  of  the  double  protection  afforded  by  the  shade  of 
the  trees  and  by  the  leafy  carpet.  If  the  trees  are  cut  away 
the  rain  splashes  down  on  the  unprotected  soil.  Most  of 
the  water  runs  off  the  surface,  often  carrying  fertile  soil 
with  it.  Even  the 'water  which  soaks  into  the  ground  is 
usually  quickly  evaporated  from  the  unshaded  surface. 


340     MAN'S  USE   AND   CONSERVATION   OF  SOILS 

In  North  America  before  the  coming  of  the  white  man, 
there  were  probably  extensive  areas  where  the  growth  of 
forests  had  been  checked  by  fires  set  by  the  Indians.  The 
prairie  regions  were  probably  much  enlarged  by  the  annual 
grass  fires.  All  this  was  done  in  order  to  make  hunting 
less  difficult.  It  is  believed  that  the  Bad  Lands  of  Dakota 
were  once  a  fertile  region  which  the  destruction  of  the  forests 


BAD  FORESTRY 
The  hillside  was  stripped,  leaving  it  a  prey  to  erosion. 

left  a  prey  to  running  water.  Erosion  has  left  these  lands 
valueless  for  agriculture.  It  is  exceedingly  difficult  even  to 
travel  over  them.  It  was  in  these  natural  fastnesses  that  the 
Sioux  Indians  made  their  last  ineffective  stand  against  the 
white  man's  civilization.  But  the  white  man  has  outdone 
the  Indian  in  reckless  destruction  of  the  forests. 

If  a  region  is  well  supplied  with  forests  so  that  the  rain 
as  it  falls  is  held  by  the  moss,  leaves,  and  roots  and  pro- 


FORESTRY 


341 


tected  from  evaporation  by  the  foliage,  soil  water  will 
continue  to  be  supplied  to  the  surrounding  open  land  long 
after  it  would  have  become  dry  had  the  forests  been  removed. 
Mountain  soils  have  been  found  which  hold  back  five  times 
their  own  weight  of  water. 

Slopes  from  which  the  forests  have  been  removed  become 
an  easy  prey  to  the  forces  of  erosion,  and  the  soil  which 


BAD  FORESTRY 
The  forest  was  razed,  leaving  no  small  trees  for  future  growth. 

for  thousands  of  years  has  been  accumulating  may  be 
swept  away  by  the  rainfall  of  a  few  seasons,  leaving  the 
slopes  bare  of  soil  and  devoid  of  vegetable  life.  Thus  the 
sites  of  valuable  forests,  which  by  proper  care  might  have 
been  continual  wealth  producers,  are  rendered  nearly 
profitless  deserts. 

The  harmfulness,  howrever,  does  not  stop  here.  The 
rain  that  falls  upon  these  slopes,  and  which  was  formerly 
retained  by  the  roots  and  vegetation,  so  that  it  slowly 


342     MAN'S  USE  AND  CONSERVATION  OF  SOILS 

crept  downward  into  the  valleys  and  streams,  now  runs 
off  quickly,  flooding  the  rivers  and  doing  damage  to  regions 
at  a  distance.  Streams  which  formerly  varied  but  little 
in  their  volume  during  the  entire  year  now  become  subject 
to  great  extremes  of  high  and  low  water.  This  renders 
them  less  useful  for  manufacturing,  commerce,  and  water 


BAD  FOBESTKY 

The  debris  was  left  to  feed  the  forest  fires  and  all  the  standing 
timber  was  ruined. 

supply,  to  say  nothing  of  the  frightful  damage  done  each 
year  by  floods. 

Not  only  is  the  destruction  of  our  forests  a  menace  to 
agriculture  and  to  river  navigation,  but  it  actually  threatens 
our  future  lumber  supply.  The  ruthless  destruction  of 
vast  forests  in  Europe  during  the  World  War  has  made  more 
imperative  than  ever  the  conservation  of  what  forests  we 
have  left  in  America. 

In  recent  years  the  demand  for  lumber  and  wood  pulp 
and  the  careless  and  wasteful  way  in  which  the  forests 
have  been  handled  by  the  lumbermen  has  greatly  reduced 


FORESTRY 


343 


the  forests  of  the  United  States.  It  has  been  authorita- 
tively stated  that  if  the  present  waste  of  our  forest  land 
continues,  the  timber  supply  of  the  country  will  be  ex- 
hausted before  1940.  Not  only  are  the  forests  being  reck- 
lessly cut  down,  but  forest  fires  are  each  year  destroying 
millions  of  dollars'  worth  of  timber.  When  the  impor- 
tance of  lumber  to  all  kinds  of  industries  is  considered, 


GOOD  FORESTRY 
Notice  how  the  underbrush  and  small  timber  has  been  cleaned  up. 

the  rapid  exhausting  of  our  forest   supplies  becomes  al- 
most appalling. 

When  the  native  forests  are  destroyed,  trees  of  other 
kinds  may  in  time  replace  those  removed,  but  frequently 
these  are  of  less  commercial  value.  Thus,  when  the  coni- 
fer forests  of  the  northern  states  are  cut  off,  birches  and 
poplars  replace  them.  If  only  the  larger  trees  had  been 
cut,  leaving  the  smaller  and  younger  trees  to  hold  the 


344     MAN'S  USE  AND   CONSERVATION   OF  SOILS 

ground,   the  more   valuable   forests  might   have   been  re- 
tained. 

The  destruction   of  the   forests  tends  also   to   extermi- 
nate the  wild    animals  and  deprives  man  of  a  chance  to 

get  away  from  his 
artificial  surround- 
ings and  obtain  a 
knowledge  and  an 
enjoyment  of  life  and 
nature  which  has 
been  unaffected  by 
his  own  dominant  in- 
fluence. 

In  many  European 
countries  the  forests 
have  become  a  na- 
tional care  and  not 
only  is  the  cutting  of 
trees,  except  under 
certain  restrictions, 
prohibited,  but  the 
greatest  care  is  main- 
tained  to  guard 
against  fires.  In  our 
own  country  the  gov- 
ernment has  recently 
established  a  number  of  forest  preserves  which  are  carefully 
patrolled,  and  here  the  destruction  from  forest  fires  is 
rigidly  guarded  against.  Great  care  of  all  forests  should 
be  taken  by  hunters,  campers,  and  all  others  who  visit 
them,  and  also  by  the  railways  passing  through  them. 
Loggers  and  lumbermen  should  see  that  it  is  to  their 


GOOD  FORESTRY 

Notice  how  carefully  the  underbrush  has 
been  removed  to  guard  against  fire. 


SUMMARY  345 

interest  to  maintain  growing  forests  and  not  wantonly  to 
destroy  them. 

SUMMARY 

The  soils  which  have  been  produced  in  one  way  or  another, 
as  described  in  Chapter  X,  are  classified  as  local  or  sedentary 
soil,  which  is  formed  from  the  rocks  directly  beneath  it ;  and 
transported  soil,  which  is  generally  brought  from  other 
localities  and  deposited  by  water,  ice,  or  wind.  Soils  are 
also  classified  according  to  the  size  of  their  particles,  as 
gravel,  sand,  silt,  and  clay.  The  best  agricultural  soils  are 
generally  of  the  consistency  of  silt,  and  are  called  loams. 

Nitrogen,  phosphorus,  and  potassium  are  the  soil  elements 
that  are  used  most  freely  by  the  growing  plant,  but  these 
elements  must  be  in  chemical  compounds  with  other  sub- 
stances before  they  are  available  as  plant  food.  Plants  also 
require  air  and  water,  and  are  dependent  on  the  activities 
of  soil  bacteria.  These  bacteria  cause  such  changes  in 
organic  matter  of  the  soil  that  it  may  be  used  by  the  plant 
as  food.  Partially  decayed  organic  matter  in  the  soil  is 
called  humus.  Humus  is  not  only  a  source  of  plant  food, 
but  also  serves  to  mellow  the  soil  and  to  conserve  soil  water. 

The  most  common  fertilizers  are  manure^.  They  contain 
nitrogen,  potassium,  and  phosphorus  in  about  the  proportions 
needed  for  ordinary  crops.  Commercial  fertilizers  contain 
one  or  more  of  the  elements  mentioned,  in  varying  pro- 
portions. The  United  States  is  now  developing  its  supplies 
of  commercial  fertilizers  and  bids  fair  to  be  independent  of 
foreign  supplies.  The  most  common  fertilizing  agents  are 
the  nitrogen-fixing  bacteria,  moles,  gophers,  and  angleworms. 

Some  plants  grow  with  their  roots  submerged  in  water, 
while  others  can  grow  only  where  the  moisture  supply  is 


346     MAN'S  USE  AND   CONSERVATION   OF  SOILS 

scant.  But  most  cultivated  crops  cannot  live  in  a  soil  that 
holds  too  much  free  water.  Land  must,  therefore,  be  prop- 
erly drained.  If,  on  the  other  hand,  drainage  is  too  free, 
it  may  wash  the  plant  food  out  of  the  soil.  Much  more 
moisture  is  lost  by  evaporation  than  by  under-drainage  or 
seepage.  In  dry  climates  or  during  droughts,  therefore, 
mulches  and  frequent  stirring  of  the  top-soil  must  be 
resorted  to  in  order  to  conserve  moisture. 

Great  areas  in  dry  climates  are  frequently  reclaimed  by 
irrigation,  while  swampy  lands  are  rendered  useful  by  drain- 
age. In  the  conservation  of  soils,  nothing  is  more  important 
than  wise  forestry.  Forests  retard  evaporation  of  soil  water, 
increase  the  underground  supplies  of  water,  and  tend  to 
prevent  great  extremes  of  high  and  low  water  in  our  rivers. 
The  ruthless  destruction  of  our  forests  also  threatens  our 
future  lumber  supply.  Our  own  government  has  been  taking 
steps  in  recent  years  to  care  for  our  forests  scientifically. 
It  deserves  the  cooperation  in  this  of  every  good  citizen. 

QUESTIONS 

Is  the  soil  in  your  neighborhood  local  or  transported?  Does 
its  character  vary  much  in  different  places  ?  Does  its  fertility  vary  ? 
Are  the  soil  particles  large  or  small? 

What  would  you  suggest  as  the  cause  of  any  soil  variations  found 
in  your  neighborhood? 

What  conditions  are  necessary  to  produce  a  fertile  soil? 

What  are  the  best  farmers  doing  to  increase  the  fertility  of  their 
soils? 

How  can  the  right  amount  of  soil  water  usually  be  maintained? 

What  steps  should  be  taken  to  guard  our  forests? 


CHAPTER  XII 
THE  SUN'S   GIFT  OF  LIGHT 

Light.  —  The  sun  is  not  only  the  source  of  almost  all 
the  heat  of  the  earth  but  also  of  its  light.  We  have  devel- 
oped artificial  self-luminous  bodies  such  as  candles,  lamps, 
electric  lights,  but  none  of  these  compares  with  the  light 
given  by  the  sun.  The  stars  also  furnish  a  little  light. 

Light  is  just  as  essential  to  life  as  heat  is.  If  plants  or 
animals  are  where  light  is  entirely  excluded,  they  begin 
to  sicken  and  die.  If  they  are  placed  where  it  is  very  cold, 
they  freeze  and  die.  Although  the  sun  gives  both  heat  and 
light,  yet  these  two  are  not  inseparable.  We  feel  the  heat 
given  out  by  boiling  water  but  there  is  no  light,  and  we 
see  the  light  of  the  moon  but  there  is  no  appreciable  heat. 
We  usually  say  that  we  feel  heat  but  cannot  see  it  and  see 
light  but  cannot  feel  it. 

Direction  of  Light  Movement.  —  Experiment  100.  —  Point 
the  pinhole  end  of  a  camera  obscura  or  pinhole  camera  (this  con- 
sists of  two  telescoping  boxes,  the 
larger  having  a  pinhole  at  the  end 
and  the  smaller  a  ground  glass  plate 
(Figure  97))  at  some  object  and  move 
the  ground  glass  plate  back  and  forth 
until  a  sharp  image  of  the  object  is  FIGURE  97 

formed.     Sketch  on  a  piece  of  paper 

the  object  and  the  image,  showing  the  direction  in  which  you  think 
the  rays  of  light  must  have  traveled  through  the  pinhole  to  form 
the  image. 

347 


348 


THE   SUN'S   GIFT    OF   LIGHT 


A  photographic  camera  is  constructed  in  the  same  way  as  this 
little  camera,  only  a  lens  is  placed  behind  the  pinhole  to  intensify 

the  image,  and  it  is 
possible  to  exchange 
the  ground  glass  plate 
for  a  photographic 
plate. 


There  are  certain 
properties  of  light 
which  seem  readily 
apparent  from  our 
daily  experiences. 
We  cannot  see  ob- 
jects in  the  dark, 
but  if  a  light  is 
brought  into  the 
room  so  that  it  can 
shine  upon  them, 
they  become  visible. 
We  see  them  be- 
cause the  light  is 
reflected  to  us  from 
them.  All  objects 
except  self-luminous 

bodies  are  seen  by  reflected  light.  Most  of  the  bodies  that 
we  know  are  dark  and  non-luminous.  Sometimes  some  of 
these  which  have  polished  surfaces  reflect  the  light  from 
a  luminous  body  and  thus  appear  themselves  to  be  furnish- 
ing light. 

An  example  of  this  is  often  seen  about  sundown  when 
the  sunlight  is  reflected  from  the  windows  of  a  house,  mak- 
ing them  look  as  if  there  were  a  source  of  light  behind  them. 


A  LAKE  MIRROR 


THE   INTENSITY   OF   LIGHT 


349 


Any  dark  body  whose  surface  reflects  light  appears  itself 
to  be  luminous  as  long  as  the  source  of  light  remains,  but 
grows  dark  again  when  the  source  is  removed.  This  is 
the  case  of  the  moon.  At  new  moon,  the  moon  is  so  situated 
with  respect  to  the  sun  that  light  is  not  reflected  to  the  earth 
and  we  cannot  see  it.  At  full  moon,  half  of  the  moon's 
entire  surface  reflects  the  sunlight,  and  it  appears  very 
bright. 

If  a  candle  is  held  in  front  of  a  mirror  and  we  look  into 
the  mirror,  we  see  the  candle  behind  it.  We  know  that 
the  candle  is  not  there  but  that  its  light  is  reflected  by  the 
mirror  in  such  a  way  as  to  make  it  appear  to  come  from 
behind  the  mirror.  We  see  the  candle  by  the  light  the  mirror 
reflects. 

If  we  wish  to  see  whether  the  edge  of  a  board  is  straight, 
we  sight  along  it.  If  we  wish  to  hit  an  object  with  a  bullet, 
we  bring  the  rifle  barrel  into  our  line  of  sight.  Wt  there- 
fore feel  confident  that  if  light  is  traveling  through  a  uniform 
medium,  such  as  air  usually  is,  it  goes  in  a  straight  line. 

The  Intensity  of  Light.  —  Experiment  101.  —  Take  two  square 
pieces  of  paraffin  about  an  inch  thick,  or  better  two  squares  of  paro- 
wax,  and  place  back  to  back 
with  a  piece  of  cardboard 
or  tinfoil  between  them. 
When  a  light  is  placed  on 
either  side  of  this  apparatus 
the  wax  toward  the  light 
will  be  illuminated,  but  not 
that  on  the  other  side  of 
the  cardboard .  (Figure  98.) 
If  lights  are  placed  on  each  side,  it  is  easy  to  see  when  both  pieces 
of  wax  are  equally  illuminated,  or  receive  the  same  amount  of 
light.  In  this  way  the  strengths  of  lights  can  be  compared. 

Place  a  candle  about  25  cm.  in  front  of  one  side  of  this  apparatus, 


FIGURE  98 


350 


THE   SUN'S   GIFT    OF   LIGHT 


and  4  candles,  placed  close  together  on  a  piece  of  cardboard  so  that 
they  can  be  readily  moved,  about  90  cm.  away  on  the  other  side. 
Move  these  candles  back  and  forth  till  a  position  is  found  where 
both  pieces  of  wax  are  illuminated  alike.  Measure  the  distance 
of  the  four  candles  from  the  wax.  How  many  times  as  far  away 
are  they  as  the  one  candle? 

The  brightness  of  the  sun's  light  is  so  great  that  even  an 
arc  light  placed  in  direct  sunlight  appears  as  a  dark  spot. 
So  great,  however,  is  the  sun's  distance  that  the  earth  re- 
ceives only  a  minute  portion,  less  than  one  two-billionth,  of 
the  light  and  heat  it  gives  out. 

The  standard  measure  for  intensities  of  light  is  the  candle 
power.  This  is  the  light  given  out  by  a  standard  candle, 


FIGURE  99 

which  is  practically  our  ordinary  No.  12  paraffin  candle. 
The  ordinary  incandescent  electric  light  is  sixteen  candle 
power.  No  comprehensible  figures  will  express  the  intensity 
of  the  sun,  using  the  candle  power  as  a  measure. 

The  intensity  of  light,  like  that  of  heat  and  electricity, 
and  all  forms  of  energy  which  spread  out  uniformly  from  their 
point  of  origin,  varies  inversely  as  the  square  of  the  distance 
from  the  source.  This  rapid  decrease  in  the  brightness  of 
light  as  the  distance  increases  is  the  reason  why  so  small  a 
change  in  the  distance  of  a  lamp  makes  so  great  a  differ- 
ence in  the  ease  with  which  we  can  read  a  book.  If  we 
make  the  distance  to  the  lamp  half  as  great,  we  increase 


REFLECTION   OF  HEAT  AND   LIGHT 


351 


the  amount  of  light  on  the  book  four  times ;  if  one  third 
as  great,  nine  times.  (Figure  99.) 

Reflection  of  Heat  and  Light.  —  Experiment  102.  —  In  a  dark- 
ened room  reflect  by  means  of  a  mirror  a  beam  of  light  from  a  small 
hole  in  the  curtain,  or  from  some  artificial  source  of  light,  on  to 
a  plane  mirror  lying  flat  upon  a  table.  If  there  is  not  sufficient 
dust  in  the  air  to  make  the  paths  of  the  rays  apparent,  strike  two 
blackboard  erasers  together  near  the  mirror.  Hold  a  pencil  ver- 
tical to  the  mirror  at  the  point  where  the  rays  strike  it.  Compare 
with  each  other  the  angle  formed  by  each  ray  with  the  pencil. 
Raise  the  edge  of  the  mirror,  and  notice  the  effect  on  the  reflected 
ray.  Place  the  pencil 
at  right  angles  to  this 
new  position  of  the 
mirror,  and  compare 
the  angles  in  each  case. 
How  do  the  sizes  of  the 
angles  on  either  side  of 
the  pencil  compare  ? 

It  has  already  been 
stated  that  the  moon 
shines  by  reflected 
light.  It  is  a  matter 
of  common  observa- 
tion that  objects  on 
the  earth  reflect  both 
heat  and  light.  In 
the  summer,  the 
walls  of  the  houses 
and  the  pavements 

of  the  streets  sometimes  reflect  the  heat  to  such  an  extent 
that  it  becomes  almost  unbearable.  In  countries  where 
the  sun  shines  brightly  nearly  all  of  the  time,  as  in  the 
Desert  of  Sahara,  reflectors  have  been  so  arranged  as 


A  REFLECTION  ENGINE 

This  engine  uses  the  rays  of  the  sun  instead 
of  coal  in  heating  its  boiler. 


352  THE    SUN'S   GIFT    OF   LIGHT 

to  reflect  the  heat  of  the  sun  on  to  boilers  to  run  steam 
engines. 

The  smooth  surfaces  of  houses  often  reflect  so  much  of 
the  light  falling  upon  them  that  the  glare  is  thrown  into 
the  windows  of  surrounding  houses  into  which  the  sun 
itself  cannot  shine.  If  one  stands  in  the  right  position,  the 
reflection  of  trees  and  other  objects  can  be  seen  in  a  smooth 
lake.  But  the  reflection  cannot  be  seen  if  the  position  of 
the  spectator  is  much  changed.  The  reflected  ray  must 
therefore  maintain  a  certain  relation  to  the  ray  that  strikes 
the  surface  from  the  object. 

In  Experiment   102,   when  the  pencil  was  held  perpen- 
dicular to  the  mirror  at  the  point  where  the  rays  touched  the 
mirror,   it   was    seen    that   both 
the  ray  from   the   window   and 
the  reflected  ray  made  about  the 
same  angle  with  it.     These  two 
FIGURE  ioo  angles  are  respectively  called  the 

angle  of  incidence  and  the  angle 

of  reflection.  By  most  careful  experimentation  it  has  been 
found  that  the  angles  between  each  of  these  two  rays,  and 
the  line  drawn  perpendicularly  to  the  reflecting  surface 
are  always  equal,  or  in  other  words  the  angle  of  reflection 
is  always  equal  to  the  angle  of  incidence.  (Figure  100.) 
This  explains  why,  if  you  are  standing  in  a  room  at 
one  side  of  a  mirror,  you  can  see  in  the  mirror  only  the 
opposite  side  of  the  room.  We  are  accustomed  to  a 
similar  law  of  reflection  when  we  bounce  a  ball  on  the  floor 
for  some  one  on  the  opposite  side  of  the  room  to  catch. 

The  Speed  of  Light.  —  In  the  latter  part  of  the  seven- 
teenth century  a  Danish  astronomer  by  the  name  of  Roemer, 


REFRACTION   OF   LIGHT  353 

after  carefully  watching  the  brightest  of  Jupiter's  satellites 
or  moons  as  it  revolved  around  the  planet,  noticed  that  the 
time  of  occurrence  of  its  eclipses  or  passages  behind  the 
planet  showed  a  peculiar  variation.  He  accurately  deter- 
mined the  interval  between  two  eclipses  or  the  time  it  took 
for  a  complete  revolution  of  the  satellite  around  the  planet. 

Using  this  interval  he  computed  the  time  at  which  other 
eclipses  should  take  place  and  found  that  as  the  earth 
in  its  revolution  around  the  sun  moved  away  from  Jupiter 
the  eclipses  appeared  to  take  place  more  and  more  behind 
time.  Determining  the  exact  time  at  which  an  eclipse 
took  place  when  the  earth  was 
nearest  to  Jupiter,  and  comput- 
ing the  time  an  eclipse  should 
take  place  six  months  later  when 
the  earth  was  farthest  from  Jupiter, 
he  found  that  the  actual  time  of 
the  eclipse  was  22  minutes  behind  FIGURE  101 

the  computed   time.      This   slow- 
ness he  said  must  be  due  to  the  time  required  by  the  light 
in  crossing  the  earth's  orbit.     (Figure  101.) 

Many  determinations  of  this  kind  have  been  made  since 
those  of  Roemer,  and  it  has  been  found  that  he  was  some- 
what in  error,  as  the  time  required  by  light  in  traveling 
across  the  earth's  orbit  is  about  16  minutes  and  40  seconds, 
or  1000  seconds.  Since  the  diameter  of  the  earth's  orbit 
is  about  186,000,000  miles  the  speed  of  light  must  be  about 
186,000  miles  per  second.  Determinations  of  the  speed 
of  light  have  been  made  in  several  other  ways  with  almost 
like  results. 

Refraction  of  Light.  —  Experiment  103.  —  Place  a  penny  in  the 
center  of  a  five-pint  tin  pan  resting  on  a  table.  Stand  just  far 


354  THE   SUN'S   GIFT    OF   LIGHT 

enough  away  so  that  the  farther  edge  of  the  penny  can  be  seen  over 
the  edge  of  the  pan.     Have  some  one  slowly  fill  the  pan  with  water. 
How  is  the  visibility  of  the  penny  affected  ? 
(Figure  102.) 

Experiment  104.  —  Fill  a  tall  jar  about 
two  thirds  full  of  water.  Place  a  glass  rod 
or  stick  in  the  jar.  Does  the  rod  appear 
straight  ?  Pour  two  or  three  inches  of  kero- 
sene on  the  top  of  the  water.  What  effect 
does  this  have  on  the  appearance  of  the  rod  ? 
FIGURE  102  Experiment  105.  —  Hold  an  ordinary  spec- 

tacle lens  such  as  is  used  by  an  elderly 
person,  or  any  convex  lens,  between  the  sun  and  a  piece  of  paper. 
Vary  the  distances  of  the  lens  from  the  paper.  The  heat  and 
light  rays  from  the  sun  are  bent  so  that  they  converge  to  a  point. 
Try 'the  same  experiment  with  a  lens  used  by  a  short-sighted 
person,  or  a  concave  lens.  This  lens  does  not  have  the  same  effect 
as  the  convex  lens.  The  rays  are  made  to  diverge.  Why  cannot 
long-sighted  and  short-sighted  persons  use  the  same  glasses  ? 

In  the  experiment  of  the  penny  in  the  dish,  the  water 
in  some  way  bent  the  ray  of  light  and  made  the  penny 
come  into  the  line  of  sight  when  it  could  not  be  seen  before 
the  water  was  there.  The  penny  was  apparently  lifted  up. 
This  illustrates  why  ponds  and  streams  look  shallower 
than  they  really  are.  This  experiment  shows  that  when 
light  is  passing  from  one  medium  to  another  it  does  not 
always  travel  in  the  same  straight  line.  Ce'rtain  media 
offer  more  resistance  to  the  passage  of  light  than  others  and 
are  called  denser  media.  It  is  this  difference  of  resistance 
which  causes  the  bending  of  the  ray. 

Suppose  that  a  column  of  soldiers  marching  in  company 
front  are  passing  though  a  corn  field  and  come  obliquely 
upon  a  smooth  open  field.  (Figure  103.)  The  men  as  they 
come  on  to  the  open  field  are  unencumbered  by  the  corn- 


LENSES 


355 


stalks  and  will  move  faster,  and  thus  the  line  of  march  will 
swing  in  toward  the  edge  of  the  corn  field.  It  can  easily  be 
seen  that  the  bending  of  the  line  would  be  in  the  opposite 
direction  if  the  soldiers  were 
marching  from  the  smooth  field 
into  the  corn  field.  If  the  com- 
pany front  were  parallel  to  the 
edge  of  the  corn  field,  then  the 
men  would  reach  the  open  field 
at  the  same  time  and  there 
would  be  no  swinging  of  the  line. 

The  above  illustration  roughly  explains  what  happens 
when  light  passes  from  one  medium  to  another.  Refrac- 
tion is  the  name  given  to  this  bending  of  light  in  passing 
through  different  media  or  through  a  medium  of  changing 
density.  Twilight,  mirage,  the  flattening  of  the  sun's 
disk  at  the  horizon,  and  other  appearances,  we  shall  find 
later,  are  due  to  this  property  of  light. 

Lenses.  —  The  bending  of  light  in  passing  from  one 
medium  to  another  has  been  turned  to  great  advantage  in 

the  use  of  lenses.  In  the 
making  of  lenses,  trans- 
parent substances  are  so 
shaped  that  when  the  rays 
of  light  strike  them,  they 
are  bent  into  any  desired 
direction.  Experiment  105 
shows  that  the  rays  may  be  brought  nearer  together 
(converged  or  focused)  or  spread  farther  apart  (diverged). 
If  the  illustration  of  the  line  of  march  of  the  soldiers  is 
kept  in  mind,  it  will  be  seen  that  the  rays  must  always 


FIGURE  104 


,356  THE   SUN'S   GIFT    OF   LIGHT 

be  bent  toward  the  thicker  part  of  the  lens.     (See  Figures 

104  and  105.) 

If  in  Experiment  100  a  convex  lens  is  placed  behind  the 

small  hole,  the  rays  of  light  from  a  large  area  will  be  focused 
on  the  ground  glass.  If  the 
plate  is  adjusted  to  the  right 
position,  a  small,  distinct  picture 
will  be  formed.  If  a  plate  cov- 
ered with  chemicals  that  undergo 


FIGURE  105  change    when    exposed   to    light 

replaces    the    ground    glass,    a 

copy  of  the  picture  is  left  upon  the  plate.  When  this  is 
developed  by  chemical  process,  permanent  pictures  may  be 
printed  from  it.  This  is  what  is  done  in  photography. 

In  the  magnifying  glass  (Figure  106)  the  eye  is  placed  near 
the  lens  and  the  rays  from  a  small  object  are  so  bent  that 
they     appear     to     be 
spread    apart    and    to 
come     from     a    much 
larger  object.     The  re- 
fracting telescope     and 

the    compound    micro-  FlQUBE  106 

scope   (Figure  93)    are 

combinations  of  magnifying  lenses  so  adjusted  as  to  produce 
the  largest  possible  clear  image  of  the  object  examined. 

Light  and  Color.  —  Experiment  106.  —  Darken  the  room  except 
for  a  small  hole  in  the  curtain  where  sunlight  may  enter.  Allow 
the  sunlight  to  pass  through  a  glass  prism  and  to  fall  upon  a  white 
wall  or  a  piece  of  white  paper.  How  has  the  white  sunlight  been 
affected?  Where  did  the  colors  come  from?  In  what  order  are 
the  colors  arranged? 

Hold  a  piece  of  red  glass  close  to  the  prism  and  between  the  prism 


LIGHT  AND   COLOR 


357 


and  the  wall  or  paper.  Do  all  the  colors  of  the  spectrum  still 
appear?  Repeat  the  experiment  with  glasses  of  other  colors.  What 
happens? 

It  was  seen  in  Experiment  106  that  when  white  light  is 
passed  through  a  prism  it  not  only  suffers  a  change  in  direc- 
tion (is  refracted),  but  it  is  also  separated  into  different 
colors.  White  light  must  then  be  made  up  of  lights  of 
different  colors,  and  the  prism  must  have  affected  these 
colors  so  that  each  was  bent  to  a  different  extent  in  passing 
through  the  glass.  (Figure  107.)  Careful  experiments  show 


FIGURE  107 

that  light  is  a  form  of  wave  motion,  and  that  the  infinitesi- 
mally  small  wave-lengths  of  the  various  colors  differ  from 
one  another.  The  colors  are  refracted  differently  in  passing 
through  the  prism  and  are  therefore  separated  from  one 
another.  The  band  of  colors  into  which  white  light  is 
separated  by  the  prism  is  called  the  spectrum. 

It  was  also  seen  that  if  the  light  from  the  prism  was  passed 
through  red  glass,  all  the  colors  except  the  red  were  cut  off, 
or  absorbed.  If  we  could  have  made  a  careful  test  of  the 
glass  we  should  have  found  that  it  had  been  warmed  by  the 
absorption  of  these  colors ;  that  is,  the  energy  of  light  had 
been  transformed  into  the  energy  of  heat.  When  light  is 


358  THE   SUN'S   GIFT   OF   LIGHT 

absorbed  its  energy  is  changed  into  heat  energy  or  chemical 
energy. 

Experiment  107.  —  Obtain  pieces  of  cloth  of  a  number  of  different 
colors.  Darken  the  room  and  light  a  Bunsen  burner.  Adjust 
the  holes  at  the  bottom  so  that  it  will  give  but  little  light.  Dip  a 
glass  rod  in  a  solution  of  common  salt  and  place  it  in  the  flame  of 
the  burner.  The  flame  will  be  colored  a  brilliant  yellow.  Now 
examine  the  colors  of  the  different  pieces  of  cloth.  Do  they  appear 
as  they  did  in  sunlight? 

The  color  of  a  non-luminous  substance  is  due  to  the  kind 
of  light  it  transmits  or  reflects.  If  a  colored  object  is  looked 
at  by  lamplight  it  will  not  appear  of  the  same  color  as  by 
sunlight  because  the  lamplight  is  deficient  in  some  of  the 
colors  of  sunlight.  Therefore  the  object  cannot  reflect  the 
same  combination  of  colors  when  exposed  to  lamplight 
that  it  reflects  when  exposed  to  sunlight. 

If,  for  example,  an  artificial  light  lacks  red  rays,  then 
a  red  surface  exposed  to  it  would  absorb  all  the  colors  of 
the  light  and  would  appear  black  because  there  are  no  red 
rays  to  be  reflected. 

By  combining  the  prism  with  the  telescope,  scientists 
have  an  instrument  for  examining  the  spectrum  of  the  sun. 
With  this  instrument  the  spectrum  is  found  to  be  crossed 
by  hundreds  of  fine  black  lines  scattered  along  the  band  of 
color.  By  bringing  known  elements  to  a  white  hot  vapor 
and  comparing  their  spectra  with  the  spectrum  of  the  sun, 
scientists  have  determined  many  substances  that  are  in  the 
sun. 

Sunlight  is  affected  by  the  air  through  which  it  comes. 
When  the  sun  sets  at  night  and  the  rays  come  to  us  through 
a  great  thickness  of  murky  air  which  is  near  the  surface  of 
the  earth,  the  light  often  appears  red  or  yellow.  The  heavy 


LIGHT  AND  COLOR 


359 


dust  and  smoke  in  the  air  has  absorbed  the  other  colors 
and  has  transmitted  one  of  these  two.  On  the  top  of  a 
high  mountain  or  on  a  clear  day,  or  when  the  sun  is  high 
overhead,  the  sky  appears  blue.  When  the  particles  of 
matter  in  the  atmosphere  through  which  light  is  coming  are 


J 


TELESCOPE  EQUIPPED  WITH  A  SPECTROSCOPE 

It  is  with  instruments  like  this  that  astronomers  have  been  able  to 
determine  the  composition  of  the  sun. 

• 

very  minute,  blue  is  the  color  reflected.     A  blue  sky  in- 
dicates a  clearer  atmosphere. 

Sometimes  after  a  shower  an  arch  appears  in  the  heavens, 
composed  of  beautiful  colors;  we  call  this  a  rainbow.  In 
this  case  the  sunlight  is  broken  into  different  colors  by  the 
drops  of  water  which  still  fall  in  the  distance,  just  as  it  is 
when  passing  through  a  prism. 


360  THE   SUN'S   GIFT    OF   LIGHT 

Sometimes  the  sun  or  moon  is  surrounded  by  bright 
rings  called,  when  of  small  diameter,  coronas,  and  when  of 
great  diameter,  halos.  These  rings  are  due  to  the  effect 
of  water  or  ice  particles  on  the  light  coming  from  the  sun 
or  the  moon. 

Under  certain  conditions  it  may  happen  that  light  com- 
ing from  objects  at  a  distance  is  so  refracted  and  reflected  by 
the  layers  of  air  of  different  density,  through  which  it  comes 


LICK  OBSERVATORY 

As  light  is  affected  by  the  atmosphere,  observatories  must  be  placed 
where  atmospheric  conditions  are  the  best.  This  famous  observatory 
is  on  a  mountain  in  the  clear  air  of  California. 

to  the  eye  of  the  observer,  that  objects  appear  to  be  where 
they,  are  not,  like  the  image  of  a  person  seen  in  a  mirror. 
This  phenomenon  is  called  mirage  or  looming.  It  occurs 
most  frequently  on  deserts  and  over  the  sea  near  the  coast. 

Sometimes  in  high  latitudes  arches  and  streamers  of 
colored,  light  are  seen  illuminating  the  northern  sky.  The 
brilliancy  and  colors  of  the  illumination  vary.  Sometimes 
it  is  bright  enough  to  be  seen  even  in  the  daytime.  This 
display  is  called  the  aurora  borealis  or  "  northern  lights  " 


LIGHT  AND   COMFORT  361 

and  is  believed  to  be  an  electrical  phenomenon  in  thin  air. 
The  heights  of  the  streamers  have  been  calculated  to  be  more 
than  a  hundred,  perhaps  several  hundred  miles,  so  that  it  is 
probable  that  air  in  a  rare  condition  extends  to  this  elevation. 

Theories  Concerning  Light.  —  Although  it  is  very  easy 
to  perceive  light  and  to  examine  many  of  its  properties, 
yet  to  determine  just  what  it  is  that  produces  the  light 
sensation  has  been  found  vastly  difficult.  Sir  Isaac  New- 
ton thought  that  light  consisted  of  streams  of  very  mi- 
nute particles,  or  corpuscles,  thrown  off  by  the  luminous 
body.  Since  about  1800,  it  has  been  considered  a  form 
of  wave  motion  which  is  transmitted  through  the  ether 
which  fills  all  space. 

Light  and  Comfort.  —  In  early  days  when  few  people  were 
able  to  get  glass  for  windows,  houses  were  dark  and  gloomy. 
At  present,  however,  glass  is  cheap  and  there  is  no  reason 
why  houses  should  not  be  well  lighted.  Few  houses  are 
built  nowadays  without  making  generous  allowance  for 
window  space.  All  modern  manufacturing  buildings  have 
the  major  part  of  their  outside  walls  devoted  to  windows. 
Hospitals  are  so  planned  that  every  possible  room  may  have 
direct  sunshine  for  at  least  a  part  of  every  day.  We  are 
beginning  to  appreciate  the  value  of  abundant  sunlight. 

Dampness  and  darkness  are  the  two  conditions  favorable 
to  the  growth  and  activity  of  bacteria.  Few  disease  germs 
can  live  if  exposed  to  the  direct  light  of  the  sun.  No  house 
can  have  too  much  sunlight.  There  should  be  no  dark 
corners  to  harbor  germs.  Kitchen  cupboards  and  sinks 
should  be  so  located,  if  possible,  that  they  may  receive  direct 
sunshine.  Bedclothes,  rugs,  hangings,  clothing,  should  all 
be  exposed  to  the  bright  sunlight  as  often  as  possible.  Sun- 


362  THE    SUN'S   GIFT   OF   LIGHT 

light  not  only  kills  disease  germs;  it  also  banishes  gloom 
and  stimulates  cheerfulness.  Cheerfulness  itself  is  a  genuine 
health  tonic. 

Up  to  about  fifty  years  ago  whale  oil  and  candles  furnished 
the  best  artificial  lights  obtainable.  It  is  difficult  for  us  to 
appreciate  how  numerous  are  the  advantages  and  how  much 


HOSPITAL  WARD 
Showing  the  great  care  taken  to  secure  light,  air,  and  cleanliness. 

greater  the  power  of  illumination  when  kerosene,  gasoline, 
acetylene,  illuminating  gas,  and  electricity  are  used.  In 
many  sections  of  our  large  cities  artificial  lighting  almost 
turns  night  into  day.  So  enormous  is  the  amount  of  fuel 
used  for  the  brilliant  lighting  of  our  cities  that  the  United 
States  Government  was  compelled  to  combine  "  lightless 
nights  "  with  "  daylight  saving  "  in  the  interest  of  fuel 
economy  during  the  World  War. 


LIGHT  AND   COMFORT  363 

Because  of  the  brilliancy  of  many  modem  artificial  lights, 
their  inferiority  to  sunlight  is  often  overlooked.  It  is  very 
difficult  to  arrange  artificial  lights  in  libraries,  schools, 
and  public  halls  so  that  work  may  be  carried  on  with  as 
great  ease  in  one  section  of  the  room  as  in  another.  Un- 
shaded high-power  lights  may  furnish  sufficient  illumina- 
tion, but  the  effect  is  too  dazzling.  Scattered  low-power 
lights  give  a  more  uniform  and  less  trying  illumination. 
Where  central  lights  are  to  be  used, 
translucent  bowls  which  diffuse  some  of 
the  light  to  the  room  and  reflect  some 
to  the  ceiling  probably  give  the  best 
results  for  general  purposes. 

It  must  be  remembered  that  if  the 
walls  and  furnishings  of  a  room  are  dark 
in  color  much  of  the  light  will  be  ab- 
sorbed and  little  reflected,  and  even 

bright    lights  wrill    illuminate    the  room 

...  AN  OLD  WHALE 

only  m  their  immediate  vicinity.     Deco-  OIL  LAMP 

rators  have  this  fact  in  mind  when  they 

recommend  lighter  walls  and  hangings  for  north  rooms  than 

for  south  rooms. 

Whatever  kind  of  illumination  is  provided,  the  person 
using  it  must  be  careful  not  only  that  his  work  shall  be 
properly  lighted  but  also  that  his  eyes  shall  be  protected 
against  direct  glare.  Too  much  care  cannot  be  taken  of  the 
eyes.  No  arrangement  of  artificial  light  is  as  easy  on  the 
eyes  or  as  reliable  as  daylight,  where  colors  are  to  be  worked 
with  or  where  careful  measurements  or  minute  adjustments 
are  to  be  made.  In  work  of  this  kind,  rooms  with  windows 
on  the  north  side,  through  which  only  diffused  light  will 
come,  are  preferable  to  rooms  lighted  by  south  windows. 


364  THE   SUN'S   GIFT   OF   LIGHT 


SUMMARY 

The  sun  is  the  source  not  only  of  almost  all  the  heat  of  the 
earth  but  also  of  practically  all  its  light.  Light  is  just  as 
essential  to  life  as  heat  is.  No  comprehensible  figures  will 
express  the  intensity  of  the  sun's  light,  using  the  candle 
power  as  a  measure.  The  intensity  of  light  varies  inversely 
as  the  square  of  distance  from  its  source. 

All  objects  except  self-luminous  bodies  are  seen  by  re- 
flected light.  Objects  on  the  earth  reflect  both  heat  and 
light.  The  angle  at  which  a  ray  of  light  is  reflected  is  equal 
to  the  angle  at  which  the  ray  strikes  the  reflecting  surface. 

Light  travels  at  the  rate  of  about  186,000  miles  per  second. 
When  it  travels  through  a  uniform  medium,  it  goes  in  a 
straight  line;  but  when  it  travels  through  media  of 
varying  densities  the  rays  are  bent  or  refracted.  The 
bending  of  light  rays  in  passing  from  one  medium  to 
another  is  turned  to  great  advantage  in  the  use  of  lenses 
which  may  be  so  constructed  as  to  bend  rays  of  light  in  any 
desired  direction. 

When  a  ray  of  white  light  is  passed  through  a  prism,  it  is 
not  only  refracted  but  is  also  separated  into  different  colors. 
Light  is  a  form  of  wave-motion,  and  the  infinitesimally 
small  wave-lengths  of  the  various  colors  differ  from  one 
another.  This  accounts  for  the  different  degrees  of  bending 
of  the  various  color  rays  when  passed  through-a  prism.  The 
band  of  colors  into  which  white  light  is  separated  is  called 
the  spectrum.  The  color  of  a  non-luminous  substance 
depends  on  the  kind  of  light  it  transmits  or  reflects.  When 
a  substance  is  brought  to  a  white-hot  vapor,  it  has  a  char- 
acteristic spectrum.  By  combining  the  prism  with  the 
"telescope,  scientists  have  an  instrument  called  a  spectroscope, 


QUESTIONS  365 

by  means  of  which  many  of  the  substances  in  the  sun  have 
been  detected. 

Changing  conditions  of  the  atmosphere  affect  the  colors 
of  sunlight  in  various  ways.  Rainbows,  halos,  coronas, 
and  mirages  are  owing  to  peculiar  conditions  of  the  atmos- 
phere, through  which  light  is  coming  to  the  eye. 

Natural  and  artificial  lighting  of  houses  deserves  the  most 
careful  consideration,  for  the  sake  of  convenience,  comfort, 
and  health. 

QUESTIONS 

What  experiences  have  you  had  which  cause  you  to  think  that 
light  travels  in  a  straight  line? 

If  a  boy  is  reading  two  feet  from  a  light  and  moves  to  a  distance 
of  eight  feet,  how  much  ought  the  strength  of  the  light  to  be  in- 
creased to  enable  him  to  read  with  the  same  ease? 

How  long  does  it  take  light  to  come  from  the  sun  to  the  earth  ? 

What  experiences  have  you  ever  had  which  illustrate  refraction  ? 

Why  do  not  colors  look  the  same  in  artificial  light  as  they  do  in 
sunlight  ? 

How  would  you  arrange  the  windows,  hangings,  and  artificial 
lights  of  a  room  to  make  it  most  healthful  and  cheerful? 


CHAPTER  XIII 
LIFE   ON  THE  EARTH 

Plants  and  Animals. — Plants  and  animals  are  com- 
binations of  the  earth's  elements  endowed  with  life.  By 
means  of  the  sun's  energy  they  are  able,  the  plants  directly 
and  the  animals  indirectly,  to  do  both  internal  and  external 
work  which  results  in  growth,  reproduction,  and  other  ac- 
tivities. Since  plants  and  animals  are  entirely  dependent 
upon  the  earth  and  sun  for  their  existence,  they,  like  other 
earth  and  sun  phenomena,  should  be  studied  in  this  course. 

Plants.  —  Although  in  their  lower  microscopical  forms  it 
is  very  difficult  to  distinguish  between  plants  and  animals, 
yet  the  forms  ordinarily  seen  differ  greatly.  Most  plants 
are  fixed  and  consist  of  root,  stem,  and  leaves,  while  most 
animals  are  movable  and  possess  a  variety  of  different  parts. 
But  some  plants,  like  the  seaweeds,  appear  to  have  no  roots ; 
some,  like  the  dandelion,  no  plant  stem,  and  some,  like  the 
cactus,  no  leaves. 

If  we  dig  around  the  base  of  a  tree,  we  find  in  the  soil  a 
network  of  roots  holding  firmly  erect  a  pillar-like  stem  with 
branches  bearing  a  profusion  of  leaves.  If  we  examine  these 
divisions  carefully,  we  shall  find  that  each  has  a  distinct  part 
to  play  in  the  life  work  of  the  tree.  We  shall  also  find  (1)  that 
plants  as  well  as  animals  need  air,  water,  and  other  kinds  of 
food,  (2)  that  plants  and  animals  take  in,  digest,  and  assimi- 
late food,  and  (3)  that  each  in  the  higher  forms  has  parts 
366 


PLANT  ROOTS 


367 


which  are  particularly 
adapted  for  doing  these 
different  kinds  of  work. 

Plant  Roots. —  Plant 
roots  usually  secure  the 
plant  to  the  ground  so 
that  the  stem  may  be 
supported.  They  also 
take  up  food  from  the 
soil  and  pass  it  on  to 
the  rest  of  the  plant. 
In  most  plants  all  the 
foods  except  carbon  and 
a  part  of  the  needed 
oxygen  are  taken  in  by 
the  roots.  The  soil  ele- 
ments that  the  plants 
must  have  are  nitrogen, 
potassium,  calcium,  mag- 
nesium, phosphorus,  sul- 
phur, and  iron.  Water 
supplies  hydrogen  and 
oxygen ;  while  carbon, 
another  necessary  ele- 
ment, is  taken  from 
carbon  dioxide  of  the 
air.  The  soil  elements 

must  be  in  soluble  chemical  combinations,  such  as  nitrates, 
phosphates,  sulphates,  and  so  on. 

Experiment  108.  —  Fill  three  2-quart  fruit  jars  each  about  half 
full  of  distilled  water.    Add  to  the  water  in  the  first  of  these  } 


THE  GRIZZLY  GIANT 

The  monarch  of  all  plants,  93  feet  around 
the  base.    Notice  the  cavalry  at  the  foot. 


368 


LIFE    ON   THE    EARTH 


gram  of  potassium  nitrate,  J  gram  iron  phosphate,  ^  gram  cal- 
cium sulphate,  and  -jffi  gram  magnesium  sulphate.  Add  to  the 
water  in  the  second  jar  the  same  ingredients  with  the  exception 
of  the  potassium  nitrate.  Replace  this  by 
potassium  chloride.  Add  nothing  to  the 
water  of  the  third  jar.  Put  the  three  jars 
where  they  will  receive  plenty  of  sunlight 
and  warmth  and  place  in  each  a  slip  of 
Wandering  Jew  about  10  inches  long.  Note 
which  slip  grows  the  most  thriftily.  In  the 
third  jar  there  is  no  mineral  food,  in  the 
first  all  of  this  food  which  is  necessary,  and 
in  the  second  all  the  necessary  food  except 
nitrogen. 

In  Experiment  108,  it  was  found  that 
in  the  distilled  water  the  plant  made 
but  little  growth.  Water  and  air 
alone  are  not  sufficient.  It  did  not 
thrive  when  the  nitrogen  was  lacking, 
but  grew  very  well  when  all  the  neces- 
sary elements  were  present.  All  plant 
foods,  however,  must  be  in  dilute  solu- 
tion before  plants  can  appropriate 
them. 

Experiment  109.  —  In  another  fruit  jar 
make  a  very  strong  solution  of  potassium 
nitrate  or,  as  it  is  commonly  called,  salt- 
peter. Place  in  this  a  slip  of  Wandering 
Jew  as  was  done  in  the  previous  experiment. 
Does  the  slip  grow  well?  It  has  a  great 

abundance  of  nitrogen,  which  was  found  so  important.  Place  in  a 
similar  strong  solution  a  growing  beet  or  radish  freshly  removed 
from  the  ground.  Notice  how  it  shrivels  up.  Place  a  similar 
beet  or  radish  in  water.  It  is  not  similarly  affected.  What  is  the 
effect  of  strong  solutions  on  plants? 


A  TYPICAL  PLANT 

Showing  root,  stem,  leaf, 
and  flower. 


PLANT   ROOTS 


ROOTS  SECURELY  HOLDING  THE  TREE  ERECT 


If  the  solution  is  too  strong,  as  seen  in  Experiment  109, 
the  plant  cannot  use  it.  This  is  the  reason  many  alkali 
soils  will  not  support 
plants.  The  alkali 
salts  are  so  readily 
soluble  that  the  soil 
water  becomes  a  solu- 
tion stronger  than  the 
plants  can  use. 

Experiment     110.  — 

Place     three    or    four 

thicknesses    of    colored 

blotting   paper  on  the 

bottom    of    a    beaker. 

Thoroughly     wet     the 

paper  and  scatter  upon 

it  several  radish  or  other  seeds.    Cover  the  beaker  with  a  piece  of 

window  glass  and  put  in  a  warm  place.    Allow  it  to  stand  for 

several  days,  being  sure  to  keep  the  blotting  paper  moist  all  the 

time.  When  the  seeds  have  sprouted,  examine  the  rootlets,  with 
a  magnifying  glass  or  low  power  microscope,  for  the 
root  hairs  which  look  like  fuzzy  white  threads.  Touch 
the  root  hairs  with  the  point  of  a  pencil.  They  can- 
not, like  the  rest  of  the  root,  stand  being  disturbed. 
On  what  part  of  the  plant  root  do  the  root  hairs  grow? 
As  the  blotting  paper  dries,  what  happens  to  the  root 
hairs  ? 

Plant  roots  are  enabled   particularly  by  the 
little  root  hairs   (Figure   108),  which  were  ex- 
amined in  Experiment  110,  to  take  the  film  of 
FIGURE  108  wa^er  which  surrounds  the  soil  particles  and  carry 
this  water  to  the  stem  and,  through  it,  to  the 
leaves.     The  water  which  the  roots  take  from  the  soil  is  a 
dilute  solution  containing  the  plant  food  substances.     Not 


370  LIFE   ON   THE   EARTH 

only  do  roots  absorb  the  water  from  the  soil,  but  they  se- 
crete weak  acids  which  aid  in  dissolving  the  mineral  sub- 
stances which  the  plants  need.  This  can  be  seen  where 
plant  roots  have  grown  in  contact  with  polished  surfaces, 
such  as  marble.  These  surfaces  are  found  to  be  etched. 

Experiment  111.  —  Cut  a  potato  in  two.  Dig  out  one  of  the 
halves  into  the  shape  of  a  cup  and  scrape  off  the  outside  skin. 
Fill  the  potato  cup  about  f  full  of  a  strong  solution  of  sugar.  Mark 
the  height  of  the  sugar  solution  by  sticking  a  pin  into  the  inside  of 
the  cup.  Place  the  cup  in  a  dish  of  water.  The  water  should 
stand  a  bit  lower  than  the  sugar  solution  in  the  potato 
cup.  After  the  cup  has  stood  in  the  water  for  some 
time,  notice  the  change  in  the  height  of  the  denser 
sugar  solution. 

Experiment  112.  — Bore  a  f-inch  hole  3  or  4  inches 
deep  in  the  top  of  a  carrot.  Scrape  off  the  outside 
skin  and  bind  several  strips  of  cloth  around  to  keep 
the  carrot  from  splitting  open.  Fit  the  hole  with  a 
one-hole  rubber  stopper  having  a  glass  tube  about  1 
meter  long  extending  through  it.  (Figure  109.)  Fill 
the  hole  in  the  carrot  with  a  strong  sugar  solution 
colored  with  a  little  eosin  and  strongly  press  and  tie 
in  the  stopper.  The  sugar  solution  will  be  forced  a 
short  distance  up  the  tube  by  the  insertion  of  the  stopper.  Mark 
with  a  rubber  band  the  height  at  which  it  stands.  Submerge  the 
carrot  in  water  and  allow  it  to  stand  for  a  few  hours.  Mark 
occasionally  the  height  of  the  column  in  the  tube.  Taste  the 
water  in  which  the  carrot  was  submerged.  There  has  been  an 
interchange  of  liquids  within  and  without  the  carrot. 

The  plant  root  takes  up  its  water  in  the  same  way  the 
water  was  taken  into  the  sugar  solution  of  the  potato  cup 
or  of  the  carrot.  The  water  or  sap  within  the  substance 
of  the  root  is  denser  than  the  soil  water,  just  as  the  sugar 
solution  was  denser  than  the  water  outside.  It  has  been 
found  that  whenever  two  liquids  or  gases  are  separated 


PLANT  ROOTS 


371 


by  an  animal  or  plant  membrane,  there  is  an  interchange 
of  the  liquids  or  gases,  the  less  dense  liquid  or  gas  passing 
through  more  rapidly.  This  is  called  osmosis  and  is  of 
the  greatest  importance  to  both  plants  and  animals. 

All  animals  and  plants  are  made  up  of  exceedingly  minute 
parts,  called  cells.  Figure  110  shows  the  cells  in  a  leaf  and  the 
leaf  hairs  greatly  magnified.  The  higher  plants  and  animals 
are  composed  of  vast  numbers  of  these  cells.  The  cell 
usually  has  a  thin  cell 
wall,  which  in  living  and 
growing  cells  incloses  a 
colorless  semi-fluid  sub- 
stance called  protoplasm. 
This  protoplasm  is  the 
living  part  of  the  plant. 
It  is  found  in  all  the  cells 
where  growth  is  taking 
place,  where  plant  sub- 
stances are  being  made, 
or  where  energy  is  being 
transformed.  It  has  the  power  of  dividing  and  forming 
new  cells,  and  it  is  in  this  way  that  the  plants  grow. 

The  little  root  hairs  are  one  kind  of  plant  cells.  They 
consist  of  a  thin  cell  wall  within  which  is  protoplasm  and 
cell  sap,  a  solution  of  different  plant  foods.  Since  the  pro- 
toplasm and  cell  sap  are  denser  than  the  soil  water,  more 
liquid  moves  into  the  cell  than  from  it.  A  little  of  the 
cell  solution  does  move  out,  however,  and  it  is  this  which 
helps  to  dissolve  the  soil  particles.  The  protoplasm  in  the 
cell  regulates  to  some  extent  the  interchange  of  liquids. 

Experiment  113.  —  Cut  off  the  stem  of  a  thrifty  geranium,  be- 
gonia, or  other  plant  an  inch  or  two  above  the  soil.  Join  the  plant 


FIGURE  110 


372 


LIFE    ON   THE    EARTH 


stem  by  a  rubber  tube  to  a  glass  tube  a  meter  long,  of  about  the 
same  diameter  as  the  stem.  See  that  the  rubber  tube  clings 
strongly  to  both  glass  tube  and  stem.  It  may  be  best  to  tie  it 
tightly  to  these.  Support  the  glass  tube  in  a  vertical  position 
above  the  stem  and  pour  into  it  sufficient  water  to  rise  above  the 
rubber  tube.  (Figure  111.)  Note  the  position  of  the 
water  column.  Thoroughly  water  the  soil  about  the 
plant.  Watch  the  height  of  the  water  column,  marking 
it  every  few  hours. 


The  water  taken  in  by  the  roots  passes  on 
from  cell  to  cell  by  osmotic  action  and  rises  in 
the  stem  in  the  same  way  that  the  water  rose 
in  the  tube  attached  to  the  stem  of  the  growing 
FIGURE  in  plant  in  Experiment  113.  The  root  pressure, 
together  with  capillarity,  as  seen  in  Experiment  97,  will 
account  for  the  rise  of  the  sap  in  lowly  plants,  but  the  cause 
of  the  rise  of  the  sap  to 
the  top  of  lofty  trees  is 
difficult  to  understand. 

Roots  extend  them- 
selves through  the  soil 
by  growing  at  the  tips. 
Here  the  cells  are  rapidly 
dividing,  forming  new 
cells,  and  building  root 
tissue.  As  water  is  so 

,.   ,    ,,  ,  FIGURE  112 

essential,  they  are  always 

seeking  it  and  extending  themselves  in  the  direction  where 
it  is  to  be  found.  This  causes  them  to  extend  broadly  and 
to  sink  deeply  (Figure  112).  A  single  oat  plant  has  been 
found  to  have  an  entire  root  extension  of  over  150  feet. 
This  seeking  of  the  roots  for  water  sometimes  causes  the 
roots  of  trees  to  grow  into  drain  pipes  and  stop  them  up. 


STEMS  373 

For  this  reason  the  planting  of  certain  trees  near  sewer  pipes 
is  often  prohibited. 

Experiment  114.  —  Boil  some  water  so  as  to  drive  out  the  air  and 
after  it  has  become  cool  fill  a  2-quart  fruit  jar  half  full.  Dissolve 
in  this  all  the  necessary  plant  food  as  was  done  hi  Experiment 
108,  making  the  solution  the  same  strength.  Place  in  this  a  slip 
of  Wandering  Jew.  Pour  over  the  surface  of  the  water  a  layer 
of  castor  oil  or  sweet  oil.  Place  this  jar  alongside  the  slip  in  the 
other  complete  food  solution,  Experiment  108.  Both  slips  have 
the  same  conditions  except  that  the  oil  keeps  out  the  air  from  the 
roots  of  one  of  them.  Does  the  absence  of  air  affect  the  growth  of 
the  slip? 

As  the  tips  of  the  roots  are  delicate,  it  can  be  readily  seen 
that  if  they  are  to  grow  readily  the  soil  around  them  must 
be  mellow.  It  was  seen  in  Experiment  114  that  if  roots 
are  to  grow  they  must  have  air,  another  reason  for  keep- 
ing the  soil  mellow. 

Roots  are,  however,  not  simply  absorbers  of  water  and 
dissolved  food.  Some  of  them  act  as  storehouses  for  the 
food  that  the  plant  has  prepared  for  future  use.  Beets, 
carrots,  parsnips,  turnips,  and  sweet  potatoes  are  examples 
of  roots  which  store  food  ready  for  the  rapid  growth  of 
the  next  year's  plant. 

Stems.  —  Experiment  115.  —  Examine  a  corn  stalk.  Notice  how 
and  where  the  leaves  are  attached  to  the  stem.  Do  the  alternate 
leaves  come  from  the  same  side  of  the  stem?  Cut  a  cross  section 
of  the  stalk.  Notice  the  outside  hard  rind,  the  soft  pithy  material, 
and  the  small  firmer  points  scattered  about  in  the  pith.  Cut  a 
section  lengthwise  of  the  stalk  and  notice  how  these  small  firmer 
points  are  related  to  the  lengthwise  structure  of  the  stem. 

Cut  off  a  young  growing  corn  stalk  and  place  the  cut  end  in 
water  colored  by  eosin  or  red  ink.  Allow  it  to  stand  for  some  time 
and  then  cut  the  stalk  off  an  inch  or  two  above  the  surface  of  the 
water.  How  have  "  the  firmer  points  "  been  affected  ?  If  possible, 


374 


LIFE   ON   THE   EARTH 


make  the  same  observations 
and  experiments  on  the  stem 
of  a  small  seedling  palm  tree. 

Experiment  116. —  Ex- 
amine a  piece  of  the  growing 
young  stem  of  a  willow,  apple 
tree  or  other  woody  stem 
that  shows  several  leaf  scars. 
Is  the  arrangement  of  the 
leaves  the  same  as  in  the  corn 
stalk?  Cut  a  cross  section 
of  this  stem  and  examine  it. 
Does  it  resemble  the  cross 
section  of  the  corn  stalk? 
Strip  off  a  piece  of  the  bark 
and  compare  it  with  the  rind 
of  the  corn  stalk.  Examine 
carefully  the  smooth,  slippery 
surface  of  the  wood  just  be- 
neath the  bark.  This  is  the 
cambium  layer. 

Examine  the  firm  wood 
beneath  this  layer.  Where  is 
the  pith  in  this  stem?  With 
a  lens  you  may  be  able  to 
see  lines  radiating  from  the 
pith  to  the  circumference  of 
the  stem.  These  are  called 
the  pith  rays.  Cut  a  length- 
wise section  of  the  stem  and 
examine  it.  Are  there  any 
fiberlike  bundles  as  in  the 
corn  stalk?  Cut  off  a  piece 
of  the  stem  already  examined 
having  the  bark  on  it,  or  a  piece  of  sunflower  stem,  and  place  the 
end  of  it  in  colored  water.  Allow  it  to  remain  for  some  time  and 
then  cut  a  cross  section  above  the  point  where  it  was  in  the  water. 


A  PINE  TREE 
Notice  the  erect  position  of  the  stem. 


STEMS  375 

Has  the  water  risen  and  colored  this  cross  section  as  it  did  the  cross 
section  of  the  corn  stalk? 

Stems  vary  greatly  in  the  positions  they  assume.  Some 
rise  firmly  erect  from  the  root,  like  the  oak  and  the  pine; 
some  cling  to  supports,  like  the  grape  and  the  ivy ;  some 
twine  around  supports,  like  the  bean ;  some  creep  upon 
the  ground,  like  the  strawberry ;  some  grow  in 
the  form  of  a  thickened  bulb  like  the  onion 
(Figure  113) ;  some,  like  the  cacti,  assume  a 
fleshy,  leaflike,  though  leafless  form ;  some,  like 
the  nut  grass,  Johnson  grass,  and  witchgrass,  Fj 
grow  underground  and  send  up  shoots,  and  some 
stems  store  up  food  underground  in  tubers,  like  the  potato 

(Figure  114),  from  which  the  next  year's 

plant  may  grow. 

Notwithstanding  all  the  diversity  shown 

by  the  stem,  its  principal  functions  are 

to  support  the  leaves,  so  that  they  will 
FIGURE  114  1,1  j    ,      .1       i-   i  ,  i 

best  be  exposed  to  the  light,  and  to  con- 
duct the  food  solutions  from  the  root  to  the  leaves.  The 
part  of  the  stem  through  which  the  cell  sap  flows  was  seen 
in  Experiments  115  and  116. 

There  are  two  great  types  of  stems,  one  represented  by 
the  corn  stalk  and  palm  and  the  other  by  the  willow,  sun- 
flower, and  bean.  On  account  of  the  structure  of  the  seeds 
these  are  called,  respectively,  monocotyledonous  (one  seed 
leaf)  and  dicotyledonous  (two  seed  leaves).  That  these 
differ  greatly  in  their  appearance  was  seen  in  Experiments 
115  and  116,  where  the  two  kinds  of  stems  were  com- 
pared. It  was  also  found  in  these  experiments  that,  in 
the  first,  the  red  colored  water  that  took  the  place  of 
the  sap  rose  in  the  fibrous  bundles  scattered  through  the 


376 


LIFE    ON   THE    EARTH 


pith,  while  in  the  second  it  rose  through  the  woody  tissue 
within  the  bark. 

Experiment  117.  —  Examine  a  cross  section  of  a  hardwood  tree 
several  years  old,  and  if  possible  of  a  palm.  Notice  the  ringlike 
arrangement  of  the  layers  in  one  and  the  absence  of  all  such  arrange- 
ment in  the  other. 

In  Experiment  117,  when  the  cross  section  of  a  dicoty- 
ledonous tree  was  examined,  it  was  found  to  be  composed 
of  circular  rings,  but  no  such  rings  are  found  in  the  cross 


A  SPLENDID  TREE  DEVELOPED  UNDER  IDEAL  CONDITIONS 

section  of  the  monocotyledonous  tree.  When  later  we 
examine  the  seeds  of  beans  and  corn,  we  shall  find  that 
they  also  differ  very  much. 

When  the  bark  is  removed  from  a  stem,  like  the  willow 
or  apple,  the  soft,  smooth  layer  underneath  is  found  to  be 


STEMS 


377 


BANYAN 

Some  of  the  branches  descend  and  take  root  in  the  ground  and  so  appear 
like  stems. 

composed  of  living  cells.     This  is  called  the  cambium  layer. 

During  the  season  of  growth,  these  cells  are  continually 

subdividing  and  forming  new  cells,  thus  adding  a  ring  to  the 

thickness    of    the    stem. 

The  age  of  a  tree  can  be 

determined    by    counting 

these    rings.      No     such 

layers  are  found   in  the 

monocotyledonous  stems. 

Grafting  (Figure  115)  and 

budding  (Figures  116  and 

117)  are  processes  of  bringing  the  cambium  layers  of  two 

trees  of  similar  kinds  in  contact  and   keeping  them  pro- 

tected   so    that   they   will   grow   together.     In   this   way, 

many  of  our  finest  species  of   fruit  are  propagated.     In 


378 


LIFE    ON   THE    EARTH 


fact,  fruit  trees  raised  from  seed  are  not  exactly  like  the 
parent  tree,  and  if  trees  are  to  be  true  to  variety  they  must 
be  propagated  in  this  way. 

Experiment  118.  —  Examine  several  growing  stems  or  twigs  which 
have  buds  upon  them  and  notice  how  the  buds  are  arranged.  Is  the 
arrangement  the  same  in  all?  If  these  buds  grew  into  twigs  or 
leaves,  would  they  shade  one  another  ?  Is  there  a  bud  at  the  end 
of  the  twig  or  stem  ? 

If  we  examine  the  tip  of  a  growing  stem  or  twig,  we 
shall  find  a  bud.  In  most  of  the  trees  and  shrubs  of  tem- 
perate regions  a  terminal  bud  is  formed  at  the  close  of 


FIGURE  116 


FIGURE  117 


the  growing  season,  and  from  this  the  shoot  continues  to 
grow  the  following  season.  Buds  are  also  found  along 
the  length  of  the  stem  and  branches,  as  was  seen  in  Ex- 
periment 118.  These  are  lateral  buds  and,  since  they  are 
usually  found  in  the  axis  of  the  leaf,  at  the  angle  formed 
by  the  leaf  and  stem,  they  are  called  axillary.  In  some 
trees  the  terminal  buds  die  at  the  end  of  the  growing  season, 


LEAVES 


379 


a,nd  the  next  year's  growth  is  due  to  one  of  the  axillary 
buds. 


Leaves.  —  If  we  examine  the  arrangement  of  the  leaves 
on  a  plant  or  tree,  we  shall  see  that  they  do  not  lie  one 
directly  above  the  other,  but  that  they  are  so  arranged  as 
not  to  shade  one  another.  Their  position  generally  is  such 
that  the  broad  upper  surface  of  the  leaf  receives  the  strong 
light  rays  perpendicu- 
larly upon  it.  To  ac- 
complish this,  the  leaves 
in  many  trees  are  ar- 
ranged spirally  around 
the  stem. 

The  stem  of  the  leaf 
itself,  in  some  parts  of 
the  tree,  often  grows 
long  and  twists  about, 
in  order  to  push  the  leaf 
out  to  the  light  and  yet 
not  let  it  be  wrenched 
away  by  the  wind.  The 
horse-chestnut  is  such  a 
leaf.  In  some  plants, 
like  the  sunflower,  the  younger  leaves  follow  the  sun  all 
day.  In  other  plants  the  rays  of  the  sun  seem  to  be  too 
bright  in  the  middle  of  the  day  and  the  leaves  are  then  held 
edgewise  to  the  light. 

A  striking  example  of  this  is  the  compass  plant,  the 
leaves  of  which  arrange  themselves  so  that  the  sun's  rays 
strike  the  broad  surface  of  the  leaves  in  the  evening  and 
morning  when  the  rays  are  not  very  strong,  but  at  noon  the 


DIFFERENT  FORMS  WHICH  LEAVES 
ASSUME 


380 


LIFE    ON   THE    EARTH 


FIGURE  118 


edge  of  the  leaf  is  toward  the  sun,  the  leaf  thus  maintaining 
a  nearly  vertical  position  all  day,  with  its  greatest  length 
extending  in  a  nearly  north  and  south  line. 
It  is  the  effort  to  regulate  the  amount  of 
light  falling  on  the  leaf,  and  not  any  mag- 
netic influence,  which  causes  the  leaf  to 
point  in  the  direction  of  the  compass  needle. 
The  shapes  of  the  leaves  vary  greatly  in 
different  plants.  Sometimes  they  assume 
very  singular  forms,  as  in  the  pitcher  plant 
(Figure  118)  and  Jack-in-the-pulpit.  Some- 
times they  even  become  carnivorous,  as  in 
the  sundew  and  Venus  flytrap. 
Around  the  margin  of  the  sun- 
dew leaf  and  on  the  inner  sur- 
face are  a  number  of  short 
bristles,  each  having  at  the  end 
a  knob  which  secretes  a  sticky 
liquid.  As  soon  as'  an  insect 
touches  one  of  these  knobs,  it 
sticks  to  the  knob  and  the  other 
bristles  begin  to  close  in  upon 
the  insect  and  hold  it  fast.  Soon 
the  insect  dies  and  the  leaf  se- 
cretes a  juice  which  digests  the 
soluble  parts  of  the  insect. 

In  the  Venus  flytrap  (Figure 
119)  the  leaf  terminates  in  a 
portion  which  is  hinged  at  the 
middle  and  has  on  the  inside 
of  each  half  three  short  hairs,  while  the  outside  is  fringed 
by  stiff  bristles.  As  soon  as  an  insect  touches  the  hairs, 


FIGURE  119 


LEAVES 


381 


the  trap  closes  rapidly  upon  it  and  stays  closed  until 
as  much  as  possible  of  the  insect  is  digested,  when  the 
trap  again  opens.  Carnivorous  plants  of  this  kind  usually 
grow  in  places  where  it  is  difficult  to  get  nitrog- 
enous foods.  As  nitrogen  is  absolutely  neces- 
sary for  the  growth  of  protoplasm  (page  371) 
these  plants  may  have  had  to  adopt  this  way 
to  supply  the  need. 

Some  leaves  extend  themselves  into  spiny 
points,  like  those  of  the  thistle  (Figure  120),  in 
order  to  keep  animals  from  destroying  the  plant, 
or  they  may  develop  a  sharp  cutting  edge,  like 
some  grasses,  or  emit  a  bad  odor,  or  have  a  repugnant, 
bitter  taste. 

The  veins  or  little  ridges  extending  through  the  leaf  from  the 
leaf  stem  vary  (Figure  121).     Sometimes  these  veins  extend 

parallel  to  one  another 
through  the  leaf,  as  in 
the  corn  and  palm.  This 
is  generally  characteris- 
tic of  monocotyledonous 
leaves.  In  other  leaves, 
the  veins  form  a  network, 
as  in  the  maple  and  apple. 
This  is  .characteristic  of 
dicotyledonous  plants. 

Experiment  119. — Place 
the  freshly  cut  stem  of  a 
white  rose,  white  carnation,  variegated  geranium  leaf,  or  any  thrifty 
leaf  which  is  somewhat  transparent,  in  a  beaker  containing  slightly 
warmed  water  strongly  colored  with  eosin.  Allow  it  to  remain  for 
some  time.  The  coloring  matter  can  be  seen  to  have  passed  up 
the  stem  and  spread  through  the  leaf  or  flower. 


FIGURE  121 


382  LIFE    ON   THE    EARTH 

The  great  function  of  the  leaf  is  to  manufacture  plant 
foods.  The  leaf  is  so  constructed  that  air  can  enter  it 
and  come  in  contact  with  its  living  cells,  as  does  the  water 
coming  up  from  its  roots.  The  circulation  of  water  in 
the  leaf  was  seen  in  Experiment  119.  There  is  in  the  living 
cell  of  the  leaf  a  green  substance  called  chlorophyll.  This 
has  the  power  to  utilize  the  energy  of  sunlight  and  to  com- 
bine the  carbon  and  the  oxygen  of  carbon  dioxide  taken 
from  the  air  with  the  hydrogen  and  the  oxygen  of  water 
taken  from  the  soil,  thus  forming  a  substance  which  prob- 
ably at  first  is  grape  sugar,  but  which  in  many  leaves  is 
changed  at  once  into  starch. 

Experiment  120.  —  Boil  a  few  fresh  bean  or  geranium  leaves  for  a 
few  minutes  in  a  beaker  of  water.  Pour  off  the  water  and  pour  on 
enough  alcohol  to  cover  the  leaves.  Warm  the  alcohol  by  putting 
the  beaker  in  a  dish  of  hot  water.  When  the  leaves  have  become 
colorless,  remove  from  the  alcohol  and  wash.  Place  the  leaves 
in  another  beaker  and  pour  on  a  solution  of  iodine.  (This  solution 
can  be  made  by  dissolving  in  500  cc.  of  water  2  grams  of  potassium 
iodide  and  \  gram  of  iodine.  The  solution  should  be  bottled  and 
kept.)  If  the  leaves  turn  dark  blue  or  blackish,  starch  is  present. 

Experiment  121.  —  Place  a  thrifty  geranium  or  other  green  plant 
in  darkness  for  two  or  three  days  and  then  treat  the  leaves  as  was 
done  in  Experiment  120.  Do  they  show  the  presence  of  starch? 
The  direct  presence  of  the  sun's  energy  in  the  form  of  light  is  neces- 
sary for  the  formation  of  starch  in  the  leaves. 

It  was  found  in  Experiment  120  that  leaves  exposed  to 
the  sun  contained  starch,  and  in  Experiment  121  that 
leaves  which  had  been  deprived  of  sunlight  did  not  have 
starch.  The  starch  disappeared  while  the  plant  was  in 
darkness.  Not  all  of  the  oxygen  from  the  carbon  dioxide 
and  the  water  is  used  in  the  manufacture  of  starch  by  the 
chlorophyll,  and  so  some  of  the  oxygen  becomes  a  waste 


LEAVES  383 

product  which  the  leaves  throw  off.     This  will  be  seen  in 
Experiment  122. 

Experiment  122.  —  Under  an  inverted  funnel  in  a  battery  jar, 
place  some  pond  scum  or  horn  wort.  Fill  the  jar  with  fresh  water 
and  over  the  neck  of  the  funnel  place  an  inverted  test  tube  filled 
with  water.  (Figure  122.)  When  placed  in  the  sunlight,  bubbles 
of  oxygen  will  rise  into  the  test  tube  and  collect.  The 
oxygen  can  be  tested  by  turning  the  test  tube  right 
side  up  and  quickly  inserting  a  glowing  splinter.  If 
the  splinter  bursts  into  a  flame,  oxygen  is  present.  (A 
freshly  picked  leaf  covered  with  water  and  put  in  the 
sunlight  will  be  seen  to  give  off  these  bubbles.)  After, 
a  small  amount  of  gas  has  been  collected  hi  the  test 
tube,  mark  the  height  of  the  water  column  and  place  _. 
the  battery  jar  in  the  dark,  allowing  it  to  remain  there 
for  ten  or  twelve  hours.  No  oxygen  is  given  off  in  the  dark. 
Place  the  jar  in  the  light  again.  Oxygen  is  given  off.  Is  the  sun's 
energy  needed  to  enable  the  plant  to  give  off  oxygen? 

The  starch  manufactured  is  insoluble  in  water  and  is 
stored  in  the  leaf  during  the  day.  But  at  night,  when 
the  leaf  is  not  manufacturing  starch,  it  is  able  to  digest 
the  starch  by  means  of  a  special  substance,  leaf  diastase, 
which  it  forms.  This  changes  the  starch  into  sugar,  which 
is  soluble  and  which  is  carried  in  solution  to  other  parts  of 
the  plant.  Compounds  such  as  starch  and  sugar,  in  which 
there  are  only  carbon,  hydrogen,  and  oxygen,  are  called 
carbohydrates. 

The  cells  in  the  leaf  and  in  other  parts  of  the  plant  have 
the  power  to  change  the  sugar  and  combine  it  with  other 
substances  contained  in  the  sap,  thus  forming  more  complex 
chemical  compounds.  These  contain  nitrogen  and  sulphur, 
besides  the  elements  of  the  sugar.  Such  compounds  are 
called  proteins.  They  are  essential  to  the  formation  of 
plant  protoplasm  and  are  very  important  as  animal  foods. 


384 


LIFE    ON   THE    EARTH 


The  digested  and  soluble  substances  which  are  prepared 
by  the  leaves  are  transported  to  other  parts  of  the  plant, 
where  they  are  combined  by  the  protoplasm  of  the  living 
cell  with  other  substances  contained  in  the  cell  sap.  Thus 
the  protoplasm  itself  is  able  to  increase  and  form  new  cells 
as  well  as  other  substances,  such  as  woody  tissue  and  oils 
and  resins.  In  forming  these  substances  the  plant  requires 


A  PINE  FOREST 
From  the  pitch  in  these  trees  turpentine  and  tar  are  made. 

oxygen  just  as  animals  do.  If  air  is  kept  from  the  roots 
of  certain  plants,  as  was  seen  in  Experiment  114,  the  plants 
cannot  live. 

These  food  substances  which  plants  make  by  using  the 
energy  supplied  by  the  sun  are  the  bases  of  all  plant  and 
animal  life.  The  sun's  energy  stored  up  in  the  green  leaf 
is  the  source  of  all  plant  and  animal  energy.  If  it  were 


LEAVES 


385 


not  for  the  leaf  manufactory  run  by  the  sun's  power,  life, 
as  we  know  it,  would  cease.  Even  plants  that  lack  chloro- 
phyll, like  the  mushroom,  must  live  on  the  food  manu- 
factured by  the  chlorophyll  of  the  green  plants. 

Experiment  123.  —  Procure  a  small,  thrifty  plant  growing  in  a 
flower-pot.  Take  two  straight-edged  pieces  of  cardboard  sufficiently 
large  to  cover  the  top  of  the  flowerpot  and  notch  the  centers  of 
the  edges  so  that  they  can  be  slipped  over  the  stem  of  the  plant 
and  thus  entirely  cover  the  top  of  the  flowerpot.  Fasten  the  edges 
of  the  cardboard  together  by  pasting  on  a  strip  of  paper.  The 
top  of  the  pot  will  now  be  entirely  covered  by  the  cardboard  but 
the  stem  of  the  plant  will  extend  up 
through  the  notches  of  the  edges. 
Cover  the  plant  with  a  bell  jar. 
(Figure  123.)  No  moisture  can  get 
into  the  bell  jar  from  the  soil  in  the 
pot,  as  it  is  entirely  covered.  Set  the 
plant  thus  arranged  in  a  warm,  sunny 
place.  Moisture  will  collect  on  the 
inside  of  the  bell  jar.  This  must 
have  been  given  out  by  the  plant 
leaves. 

Since  all  the  processes  of  form- 
ing new  material  by  the  plant 
require  large  amounts  of  water, 
it  can  readily  be  seen  why  water  is  so  essential  to  plant 
development.  The  water  from  which  the  food  materials 
have  been  taken  is  thrown  off  by  the  leaves,  as  seen  in 
Experiment  123.  The  amount  of  water  thus  thrown  off  by 
plants  is  very  great.  A  single  sunflower  plant  about  six 
feet  tall  gives  from  its  leaves  about  a  quart  of  water  in  a 
day,  and  an  acre  of  lawn  in  dry,  hot  weather  gives  off  prob- 
ably six  tons  of  water  every  twenty-four  hours. 

If  the  water  passes  out  of  a  plant  too  rapidly  so  that 


FIGURE  123 


386 


LIFE    ON   THE    EARTH 


there  is  not  enough  left  to  provide  for  the  making  and 
transporting  of  the  food,  the  work  of  the  plant  cannot  be 
carried  on,  and  the  plant  dies.  It  is  on  account  of  this 
that  many  plants  are  especially  prepared  to  retain  their 
water  supply.  In  almost  all  plants  the  stoniata,  or  little 
pores  in  the  leaf  through  which  the  wrater  passes  out,  close 
up  when  too  much  water  is  being  lost. 

In   some  plants,   like  the   corn,   when   the  root  cannot 
supply    sufficient   moisture,    the   leaves   curl  up  and  thus 

present  less  surface  for 
evaporation.  In  trees 
like  the  eucalyptus  the 
leaves  hang  vertically 
wiien  the  sun  gets  too 
bright  and  present  their 
edges  to  the  sun's  rays. 
Some  leaves,  like  the 
sage,  are  especially  pre- 
pared to  conserve  their 
moisture  by  having  their 
surfaces  covered  with 
hairs.  Others  have  a 
waxy  covering,  as  the 
cabbage  and  the  rubber 
tree.  In  some  plants  the  leaves  are  very  small  and  have 
few  pores,  as  the  greasewood  of  the  desert,  and  some  have 
done  away  with  leaves  altogether,  as  the  cactus.  It  is 
because  the  roots  cannot  supply  sufficient  moisture  where 
the  ground  freezes  in  the  winter  that  trees  having  large 
leaves  shed  them.  Only  trees  like  the  pine,  whose  needle- 
like,  waxy  leaves  give  off  almost  no  moisture,  can  retain 
their  leaves. 


A  SUNFLOWER  PLANT 


FLOWERS 


387 


Flowers.  —  The  stem  not  only  bears  leaves  but,  in  the 
higher  kinds  of  plants,  it  bears  flowers.  The  function 
of  the  flower  is  to 
produce  seeds  and 
provide  for  the  con- 
tinued existence  of  its 
kind.  If  the  flower 
of  a  buttercup,  quince, 
cassia,  or  geranium  is 
examined,  it  will  be 
found  to  be  made  up 
of  four  distinct  kinds 
of  structures. 

Around  the  outside 
is  a  cluster  of  greenish 
leaves.  This  is  called 
the  calyx.  Within  the 
calyx  is  the  corolla, 

a     Cluster     of     leaves  EUCALYPTI  LEAVES 

which  in  many  plants  are  colored.  Within  the  corolla  are 
a  number  of  parts  consisting  of  a  rather  slender  stalk  with 
an  enlarged  tip.  This  tip  is  called  the 
anther,  and  the  stalk  and  anther  together, 
the  stamen. 

In  the  center  of  the  flower  are  the  pistils. 
At  the  top  of  a  pistil  is  generally  a  some- 
'   what  enlarged  portion,  the  stigma,  which  is 
SHOW-    sticky  or  rough ;   and  at  the  bottom  there 
is   an   enlarged    hollow   portion,    the   seed- 
bearing  part,  called  the  ovary.    These  two 
parts  are  connected  by  the  stalklike  style.    The  stamens 
and  pistils  are  the  essential  parts  of  the  flower,  the  calyx 


FLOWER 

ING  DIFFERENT 
PARTS 


388 


LIFE    ON   THE    EARTH 


PINK  GENTIAN 

Showing  the  anthers,  which  are  covered  with 
pollen. 


and  corolla  being  simply  for  protection  or  assistance.     All 
flowers  do  not  have  these  four  parts,  but  every  flower  has 

either  stamen  or  pis- 
tils or  both. 

The  anther  pro- 
duces a  large  num- 
ber of  little  granular 
bodies,  called  pollen 
grains,  each  of  which 
consists  of  a  free 
cell  containing  proto- 
plasm. When  the 
pollen  grains  are  ripe, 
the  anther  opens  and 
exposes  them.  If  a 
pollen  grain  of  the  right  kind  falls  upon  a  stigma  it  grows  and 
sends  down  a  tiny  tube  through  the  style  into  the  ovary, 
where  a  little  proto- 
plasmic cell,  called  the 
egg  cell,  has  been  pro- 
duced. The  essential 
parts  of  these  two  differ- 
ent kinds  of  protoplasms 
unite  and  a  new  cell  is 
formed. 

This  new  cell  grows 
and  divides  into  more 
cells,  thus  forming  the 
young  embryo  of  a  new 
plant.  This  embryo  is 
the  living  part  of  the 
seed  and  around  it  usu-  MINT  FLOWER 


FLOWERS 


389 


ally  a  great  deal  of  plant  food  is  stored,  so  that  when  it 
begins  to  grow  it  will  have  plenty  of  nourishment  until  it  is 
able  to  develop  the  roots 
and  leaves  necessary  to 
prepare  its  own  food. 

Embryos  cannot  be 
produced  unless  pollen 
grains  and  egg  cells  unite, 
so  it  is  absolutely  essen- 
tial that  the  right  kind  of 
pollen  grains  be  brought 
to  the  stigma.  Some- 
stigmas  are  able  to  use 
the  pollen  grains  pro- 
duced by  the  anthers  of 
their  own  flowers,  but 
others  can  only  use  pollen 
from  other  flowers  and 
other  plants.  It  is  there- 
fore necessary  that  these 
pollen  grains  be  carried 
about  from  flower  to 
flower  if  fertile  seeds  are 
to  be  produced. 

In  some  cases  the  pol- 
len is  borne  about  by  the 
wind,  as  in  the  case  of 
corn.  In  this  way  an  exceedingly  large  number  of  pollen 
grains  are  wasted,  as  can  be  seen  by  the  great  amount  of 
yellow  pollen  scattered  over  the  ground  of  a  cornfield  when 
the  corn  is  in  bloom.  In  the  corn  each  one  of  the  corn 
silks  is  a  pistil  and  a  seed  is  produced  at  its  base  if  a  pollen 


ill// 


J 


EAR  OF  CORN 


Each  kernel  is  the  result  of  a  wind-blown 
pollen  grain  falling  upon  a  corn-silk. 


390  LIFE    ON   THE   EARTH 

grain  lights  upon  the  stigma  at  its  upper  extremity.  The 
flowers  of  walnut  and  apple  trees  are  fertilized  by  wind- 
blown pollen. 

The  pollen  of  very  many  plants,  however,  is  carried 
about  by  humming  birds,  bees,  and  other  insects.  As 
the  bee  crawls  into  the  flower  to  get  the  nectar  at  the 
bottom,  it  brushes  against  the  anther  and 
some  of  the  pollen  grains  become  at- 
tached to  it.  These,  later,  are  rubbed  off 
by  the  rough  or  sticky  stigma  of  another 
flower  which  the  bee  enters  and  thus  the 
flower  is  fertilized.  The  humming  bird, 
by  reaching  its  long,  slender  beak  down 
into  the  long,  narrow  tube  formed  by  the 
corolla  of  the  "  wild  honeysuckle  "  (Figure 
124),  brushes  upon  the  stigma  the  pollen 
grains  it  has  obtained  from  another  flower 
and  thus  distributes  pollen  from  flower  to 
flower.  In  no  other  way  could  these 

FIGURE  124 

plants  be  fertilized. 

The  beautiful  colors  of  flowers  and  the  sweet  nectars 
that  many  of  them  secrete  are  the  adaptations  of  the  plant 
for  enticing  insects  to  enter  them  and  bring  to 
their  stigma  the  pollen  from  other  flowers,  or 
take  from  their  anthers  pollen  needed  to 
fertilize  another  similar  plant. 

FIGURE  125 

Some  flowers  are  so  constructed  that  only 
certain  insects  can  fertilize  them;  the  wild  honeysuckle 
requires  the  humming  bird,  the  red  clover  the  bumblebee 
(Figure  125),  and  other  plants,  other  kinds  of  insects. 
Flowers  of  some  varieties  of  plants  cannot  be  fertilized  by 
flowers  of  a  like  variety.  Certain  varieties  of  strawberries, 


FLOWERS  391 

for  example,  need  to  have  other  varieties  planted  near  them, 
if  they  are  to  prosper.  Some  plants  need  not  only  to  have 
other  varieties  planted  near,  but  they  also  require  the  pres- 
ence of  special  insects. 

One  of  the  most  striking  examples  of  this  is  the  Smyrna 
fig.  For  many  years  attempts  were  made  to  introduce 
this  fig  into  California.  The  trees  grew  but  the  fruit  did 
not  mature.  It  was  then  observed  that  in  the  regions  where 
this  fig  was  successfully  grown  a  species  of  wild  fig  was 
abundant  and  that  the  natives  were  accustomed  to  hang 
branches  of  the  wild  fig  in  the  Smyrna  fig  trees  at  the  time 
they  were  in  flower.  These  wild  fig  trees  were  brought  to 
California  and  grown  near  the  Smyrna  fig  trees,  but  still 
figs  did  not  mature.  Upon  further  examination  it  was 
observed  that  at  the  time  of  flowering  a  small  insect  issued 
from  the  wild  figs  and  visited  the  flowers  of  the  Smyrna  figs. 
This  insect  was  brought  to  California  and  now  it  is  possible 
to  grow  figs.  The  flower  of  the  Smyrna  fig  has  no  stamen  and 
it  is  necessary  for  the  wild  fig  to  furnish  the  pollen  which 
is  only  successfully  carried  to  the  stigmas  of  the  edible  fig 
by  the  small  fig-fertilizing  insect. 

A  somewhat  similar  case  is  that  of  the  yucca  found  in 
the  dry  region  of  southwestern  United  States.  This  flower 
can  be  fertilized  only  by  the  aid  of  a  small  moth  which  flies 
about  at  night  from  flower  to  flower.  It  enters  the  flower, 
descends  to  the  bottom,  stings  one  of  the  ovaries,  deposits 
an  egg,  then  ascends  and  crowds  some  pollen  on  the  stigma. 
The  grub,  when  it  hatches  from  the  egg,  feeds  on  the  seeds 
in  the  ovary,  but  as  there  are  many  seeds  in  the  flower 
which  have  been  fertilized  and  the  grub  eats  only  a  few  of 
these,  the  moth  has  made  it  possible  for  the  yucca  to  pro- 
duce seeds  sufficient  for  its  continued  propagation,  which 


392 


LIFE    ON    THE    EARTH 


would  be  impossible  if  it 
were  not  for  the  moth. 

These  are  only  a  few  of 
the  vast  number  of  cases 
which  show  the  close  re- 
lationship existing  between 
plants  and  animals  and 
the  dependence  of  the  one 
upon  the  other. 

Seed  Dispersal.  —  Not 

only  must  flowers  produce 
fertile  seeds,  if  the  plants 
are  to  continue  to  exist, 
but  these  seeds  must  be 
scattered.  To  do  this  the 
seed  pods  of  some  plants 
suddenly  snap  open  and 
spread  their  seeds.  The 
touch-me-not  and  pea  are 
examples  of  this.  In  some 

plants,  like  the  maple,  the  seeds  are  winged  (Figure  126)  and 

float  for  some  distance  in  the  air.     Others,  like  the  thistle 

and  the  dandelion,  have  light,  hairlike 

appendages  which  enable  them  to  float 

away.     In  the  case  of  the  tumbleweed 

(Figure  127)   the  plant  itself   is  blown 

about,  scattering  the  seeds  over  the  fields 

as  it  bumps  along  from  place  to  place. 
Some  seeds  are  provided  with  hooks  or  barbs,  like  the 

beggar's-ticks  (Figure  126),  which  attach  the  seeds  to  animals 

so  that  they  are  carried  to  a  distance.     Seeds  having  an 


YUCCA  OR  SPANISH  BAYONET 


FIGURE  126 


SEEDS  AND   THEIR  GERMINATION 


393 


FIGURE  127 


edible  fruit  cover,  such  as  the  cherry,  blackberry,  and  plum, 
are  eaten  by  birds  and  animals  and  the  undigested  seed 
deposited  far  away  from  the  place 
where  the  seed  grew.  Seeds  like 
the  acorn  are  carried  about  by 
squirrels  and  other  animals.  Many 
seeds  are  able  to  float  in  water  for 
a  considerable  time  without  being 
injured  and  are  borne  about  by 
currents.  Shores  of  streams  and  islands  receive  many  of 
their  plant  seeds  in  this  way.  The  cocoanut  palm  is  a  no- 
table seed  of  this  kind -and  is  found  widely  scattered  over 
tropical  islands. 

Seeds  and  Their  Germination.  —  Experiment  124.  —  Take 
two  common  dinner  plates  and  place  in  the  bottom  of  one  of  them  two 
or  three  layers  of  blotting  paper  and  thoroughly  wet  it.  Place  some 

wheat  or  other  kinds  of 
seeds  upon  this.  Now  in- 
vert the  other  plate  over  the 
first,  being  careful  to  have 
the  edges  touch  evenly. 
This  makes  a  moist  chamber 
and  gives  the  most  favor- 
able conditions  for  ger- 
mination. Do  all  the  seeds 
germinate  at  the  same  time? 
Does  the  position  of*  the 
seed  make  any  difference? 
What  takes  place  first  in 
the  process  of  germination? 
What  appears  first,  the  leaf 
or  the  root  ?  Why  does  the 
seed  shrivel  up? 

SCRUB  OAK  BRANCH  Experiment    125.  —  Cut 

Showing  the  acorns.  open  several  seeds,  such  as 


394  LIFE   ON   THE   EARTH 

pumpkin,  squash,  bean,  corn,  and  drop  on  to  the  inside  of  each  a  few 
drops  of  the  iodine  solution  made  in  Experiment  120.  Do  the 
seeds  show  the  presence  of  starch? 

Experiment  126.  —  Soak  some  beans  for  about  twenty-four  hours. 
Rub  off  the  skin  from  two  or  three  and  examine  their  different  parts 
carefully.  Plant  the  beans  in  a  box  of  damp  sawdust.  Put  the 
box  in  a  warm  place.  Plant  some  corn  that  has  been  soaked  for 
two  or  three  days  in  the  same  box.  After  the  seeds  have  been 
planted  several  days,  carefully  remove  a  bean  and  a  grain  of  corn 
and  examine.  Make  a  sketch  of  each  of  the  seeds. 

After  a  few  days  more  remove  another  seed  of  each  and  examine 
and  sketch.  Continue  to  do  this  until  the  little  plants  have  be- 
come quite  well  grown.  Do  the  two  seeds 
develop  alike?  Which  of  the  seeds  has  two 
similar  parts?  These  two  parts  are  called 
cotyledons.  What  appears  to  be  the  use  of  these 
parts  to  the  sprout?  Consult  the  results  of 
Experiment  124.  Note  the  root  development 
in  each  seed  and  the  stem  development.  The 
sprouts  get  their  food  from  the  seed. 


When  we  examined  the  different  seeds 
in  Experiment  125,  we  found  that  they 
each  contained   starch.     When  the  seeds 
were  soaked  and  planted,  we  found  that 
a  part  of  the  seeds  began  to  grow,  form- 
ing a  sprout.     This  part  is  the   embryo 
already  described.    We  also  saw  that  the  bean  seed  divided 
into  two  like  parts  which  gradually  withered  and  shrank, 
as  the  sprout  grew,  while  the  corn  had  only  one  such  part. 

These  parts  are  called  cotyledons,  or  seed  leaves.  The 
bean  seed  (Figure  128)  is  a  dicotyledon  (two  seed  leaves) 
and  the  corn  a  monocotyledon  (one  seed  leaf).  These  coty- 
ledons are  the  food  storehouses  for  the  germinating  seed. 
As  the  sprout  grew,  the  root,  with  its  root  hairs,  developed, 


SEEDS  AND   THEIR  GERMINATION  395 

and  the  stem  with  its  leaves.  When  these  had  grown  strong 
enough,  the  cotyledons,  having  performed  their  part,  dropped 
off.  The  plant  was  now  ready  to  prepare  its  own  food  by 
the  aid  of  the  sunlight. 

Experiment  127.  —  Place  several  beans  in  a  tumbler  of  damp  saw- 
dust and  put  it  in  a  warm,  light  place.  Keep  the  sawdust  moistened. 
After  the  beans  are  well  sprouted,  with  a  sharp  knife  cut  one  of  the 
half  beans  or  cotyledons  off  from  a  sprout.  Cut  both  cotyledons 
off  another  sprout.  Put  the  sprouts  back  on  the  sawdust.  Do 
the  sprouts  grow  as  well  as  those  of  the  other  beans? 

Experiment  128.  —  Fill  a  16-ounce,  wide-mouth  bottle  about  one 
third  full  of  peas  or  beans.  Pour  in  more  than  enough  water  to 
cover  them.  Tightly  cork  the  bottle  and  put  in  a  warm,  sunny 
place.  Put  another  similar  corked  empty  bottle  beside  it.  Allow 
the  bottles  to  stand  for  several  days  until  the  peas  have  sprouted. 
Remove  the  cork  from  the  bottle  containing  the  peas  and  insert 
a  burning  splinter.  Do  the  same  to  the  empty  bottle.  Why  does 
not  the  splinter  burn  as  well  in  each  ?  If  on  being  placed  in  either 
bottle  the  splinter  is  smothered  out,  it  shows  the  presence  of  carbon 
dioxide. 

Experiment  129.  —  Fill  two  8-ounce,  wide-mouth  bottles  each 
about  one  third  full  of  coarse  sawdust  and  fill  the  remaining  part 
with  peas  which  have  been  soaked  for  a  day.  Pour  in  sufficient 
water  to  cover  the  sawdust.  Cork  one  of  the  bottles  tightly,  leaving 
the  other  open.  Put  the  two  bottles  in  a  warm,  sunny  place. 
Whenever  necessary,  pour  on  sufficient  water  to  keep  the  sawdust 
in  the  open  bottle  wet.  In  which  bottle  do  the  seeds  sprout  the 
better?  Does  air  appear  to  be  necessary  for  the  growth  of  seeds? 
As  determined  by  the  previous  experiment,  what  part  of  the  air 
is  used? 

We  found  in  Experiment  127  that  if  the  cotyledons 
were  cut  off  before  the  sprout  had  become  sufficiently 
mature,  it  could  not  continue  its  growth.  In  Experiment 
128  we  found  that  the  sprouting  seeds  took  up  oxygen 
from  the  air  and  gave  out  carbon  dioxide  just  as  animals 


396  LIFE   ON   THE   EARTH 

do.  Energy  was  needed  and  this  energy  was  obtained  by 
combining  the  carbon  in  the  seed  with  the  oxygen  in  the 
air,  as  it  is  when  wood  is  burned.  We  found  in  Experi- 
ment 129  that  the  seeds  could  not  sprout  well  unless  suffi- 
cient air  was  supplied.  That  was  because  there  was  not 
enough  oxygen  supplied  to  furnish  the  necessary  energy. 

Experiment  130.  —  Place  several  sprouted  seeds  in  each  of  two 
tumblers  nearly  filled  with  damp  sawdust.  Put  these  tumblers 
side  by  side  in  a  warm,  light  place.  Cover  one  of  the  tumblers 
with  a  box  painted  black  so  as  to  exclude  the  light.  In  which  do 
the  seeds  grow  the  better? 

After  the  seeds  were  sprouted  and  had  begun  to  pre- 
pare their  own  food,  it  was  found  in  Experiment  130  that 
they  were  not  able  to  do  this  unless  exposed  to  the  light 
of  the  sun.  The  parent  plant  had  stored,  in  a  latent  form 
in  the  seed,  energy  which  it  had  received  from  the  sun. 
This  potential  energy  the  sprout  was  able  to  change  into 
the  kinetic  form  by  the  aid  of  oxygen,  and  to  use  in  the 
work  of  growing.  After  this  latent  energy  had  been  ex- 
pended, it  had  to  fall  back  upon  the  direct  energy  of  the 
sun  which  came  to  it  in  the  form  of  sunlight. 

Dependent  Plants.  —  Experiment  131.  —  Expose  a  piece  of 
moist  bread  to  the  air  for  a  short  time  and  then  put  it  into  a  covered 
dish  so  as  to  retain  the  moisture.  Does  any  change  take  place  in 
the  bread?  Examine  with  a  magnifying  glass  the  mold  which  ap- 
pears. 

Experiment  132.  —  (1)  Bruise  a  sound  apple  and  place  the  bruised 
part  in  contact  with  a  thoroughly  rotten  apple.  Wrap  the  two  up 
together  in  a  wet  cloth  and  put  in  a  fruit  jar.  Seal  the  jar  to  prevent 
the  water  from  evaporating.  (2)  Plunge  a  pin  repeatedly  first 
into  a  rotten  apple  and  then  into  a  sound  one.  Wrap  the  sound 
apple  in  a  wet  cloth  and  seal  in  a  fruit  jar.  (3)  Place  a  lemon 
which  has  developed  a  green,  spongy,  rotten  place  in  it  in  contact 


DEPENDENT  PLANTS 


397 


with  a  perfect  lemon  and  keep  them  where  they  will  be  moist. 
What  happens  to  the  sound  fruits? 

The  plants  that  we  have  so  far  studied  are  green  plants 
and  contain  chlorophyll.  They  are  able  to  prepare  their 
food  from  the  air  and  soil  by  the  aid  of  the  sun's  energy. 
There  is,  however,  another  great  group  of  plants  which 
may  be  called  dependent  plants.  They  have  no  chlorophyll 


MISTLETOE  GROWING  ON  AN  OAK 
An  interesting  parasitic  plant. 

and  are  obliged  to  live  upon  the  food  that  green  plants  have 
prepared.  They  find  this  food  either  in  the  living  or  in  the 
dead  parts  of  plants  or  animals,  the  animals  having  digested 
it  from  plants  or  other  animals,  who  originally  obtained  it 
from  plants.  If  plants  live  upon  "living  plants  or  animals, 
they  are  called  parasites,  if  upon  dead  ones,  saprophytes. 
We  are  most  of  us  familiar  with  some  of  the  larger  de- 


398 


LIFE    ON   THE    EARTH 


FIGURE  129 


pendent  plants,  or  fungi,  such  as  the  mushrooms  (Figure 
129)  and  toadstools.  Mushrooms  are  widely  used  as  a  deli- 
cacy and  their  growth  is  an  important  industry  in  some 
sections.  They  are  grown  in  soils  very  rich  in  humus  and 
generally  in  dark,  cellarlike  places.  The 
mushrooms  that  grow  wild  in  the  woods 
are  abundant  in  some  localities  but 
should  not  be  used  for  food  unless  most 
carefully  examined  by  some  one  who 
is  expert  in  determining  the  different 
species.  There  are  several  species  of 
mushrooms  which  are  exceedingly  poison- 
ous. For  one  of  these  there  is  no  known  antidote.  The 
general  structure  of  these  larger  fungi  can  be  seen  by 
examining  a  mushroom  obtained  from  the  market. 

The  bacterium  is  a  single-celled  de- 
pendent plant,  probably  the  simplest 
of  all  plants ;  it  can  be  seen  only  with 
a  high-power  microscope.  Bacteria 
are  rod-shaped,  thread-shaped,  screw- 
shaped,  or  have  various  other  forms 
(Figure  130).  The  protoplasm  in  the 
cell  of  bacteria  has  the  power  to  as- 
similate food  and  build  more  proto- 
plasm. When  the  cell  has  grown 
sufficiently,  it  divides  into  two  cells. 

A  healthy  bacterium  grows  fast 
enough  to  be  ready  to  divide  about 
once  an  hour.  If  it  divided  once  an  hour  and  each  division 
continued  to  divide  once  an  hour,  in  the  course  of  twenty- 
four  hours  there  would  be  nearly  seventeen  million  bacteria 
produced.  If  this  were  kept  up  for  some  weeks,  the  mass 


FIGURE  130 


ANIMALS  399 

of  bacteria  would  be  as  large  as  the  earth.  Of  course,  this 
would  mean  that  each  bacterium  had  plenty  of  room  to 
live  in  and  plenty  of  food  to  live  on  and  nothing  to  injure 
it.  These  conditions  are  not  found,  and  each  bacterium  has 
to  struggle  for  existence  just  as  every  other  plant  does. 
As  it  is,  however,  bacteria  are  numberless. 

Some  of  the  activities  of  soil  bacteria  we  have  already 
studied.  There  are  many  other  kinds  of  bacteria,  and  the 
relations  of  many  of  them  to  man  are  of  such  importance 
that  they  will  be  given  further  attention  in  another  chapter. 

Molds  are  made  up  of  many  cells,  and  reproduce  them- 
selves by  producing  spores.  If  the  mold  on  bread  is  allowed 
to  grow  for  a  long  enough  time  under  favorable  circumstances, 
you  will  note  a  fine  black  powder  that  forms.  The  par- 
ticles of  this  powder  are  spores  (seedlike  bodies)  which  will 
themselves  grow  into  molds  if  favorable  conditions  are 
offered.  Mushrooms  reproduce  by  means  of  spores. 

Yeasts  are  single-celled  plants,  as  are  bacteria,  but  they 
do  not  increase  as  bacteria  do.  A  little  bud  forms  on  the 
side  of  the  yeast  cell,  which  grows  until  it  finally  separates 
from  the  parent  cell.  In  this  way  a  single  yeast  cell 
may  produce  several  other  yeast  cells,  whereas  a  single 
bacterium  may  only  divide  into  two. 

Animals.  —  Animals  do  not  take  their  energy  directly 
from  the  sunlight,  but  indirectly  from  the  latent  energy 
stored  up  in  the  foods  prepared  by  green  plants.  These 
foods  may  be  eaten  as  stored  by  the  plants,  or  they  may 
have  passed  through  the  medium  of  other  plants  and  an- 
imals. The  energy  thus  stored  up  is  liberated  by  com- 
bining the  carbon  with  oxygen.  Carbon  dioxide  is  frn-.l. 

The  green  plants  use  this  carbon  dioxide  again  and,  by 


400 


LIFE    ON   THE    EARTH 


the  aid  of  the  sun's  energy,  free  the  oxygen  and  store  up 
the  carbon.  Thus  the  cycle  goes  on,  over  and  over,  the 
plants  freeing  oxygen  and  taking  up  carbon  dioxide,  and 
the  animals  freeing  carbon  dioxide  and  taking  up  oxygen. 
The  cells  of  plants  which  feed  upon  the  food  prepared  by 
the  chlorophyll  of  the  leaves  use  oxygen  and  give  out  carbon 
dioxide  just  as  the  animal  cells  do ;  so  also  do  other  plants 
to  some  extent. 

Classification  of  Animals.  —  For  convenience  of  study 
the  animal  kingdom  has  been  divided  into  two  great  classes 
—  the  invertebrates  (without  backbone)  and  the  vertebrates 
(with  backbone).  The  invertebrate  is  the  much  more 
numerous  class  as  it  contains  the  worms,  shellfish,  insects, 

and  those  almost  countless 
forms  of  animal  life  which 
have  no  internal  bony  skele- 
ton and  backbone.  The 
higher  animals,  like  fishes, 
amphibia,  reptiles,  birds,  and 
mammals,  belong  to  the 
class  of  vertebrates.  Man 
himself  is  the  highest  of  the 
vertebrates,  and  his  struc- 
ture will  be  studied  later. 

GLOBIGERINA  (Greatly  magnified)  Invertebrates  :      Protozoa. 

—  The  very  lowest  forms  of 
animal  life,  the  protozoa, 
are  single-celled  animals.  In  some  species  they  are  very 
difficult  to  distinguish  from  plants  of  the  lowest  orders. 
They  are  microscopic  in  size  and  most  of  them  live  in  water. 
Some  of  these  tiny  protozoa  living  in  the  sea  are  covered 


The  shells  of  these  minute  animals 
cover  much  of  the  ocean  floor. 


WORMS  401 

by  an  extremely  thin  shell  of  lime.  When  they  die,  their 
shells  sink  to  the  bottom  of  the  sea.  So  rapidly  do  these 
animals  multiply  that  their  minute  shells  have  made  thick 
layers  of  chalk  like  the  famous  chalk  cliffs  of  the  south 
of  England. 

Our  chief  interest  in  protozoa  in  the  present  study  is  that 
certain  of  them  are  the  cause  of  several  kinds  of  disease  which 
can  readily  be  prevented  with  proper  care.  Malaria  and 
the  terrible  African  disease  called  sleeping  sickness,  and 
probably  yellow  fever,  are  caused  by  these  little  animals. 
We  shall  study  them  more  fully  later  in  connection  with 
harmful  bacteria. 

Worms.  —  Another  class  of  invertebrates  is  the  worms. 
One  of  these,  the  earthworm,  was  found  in  the  study  of 
soil  making  to  be  very  important  and  should  be  considered 


EARTHWORM 
A  great  helper  to  the  farmer. 


in  this  place.  If  an  earthworm  is  examined,  it  will  be 
seen  that  the  body  is  made  up  of  segments  or  rings,  and 
that  it  moves  by  successively  shortening  and  elongating 
its  body.  Extending  through  the  middle  of  the  body  is 


402 


LIFE    ON   THE    EARTH 


an   alimentary   canal   consisting   of   a   mouth,   gizzard   for 
grinding  food,  stomach,  and  intestines. 

Near  the  head  is  a  little  nerve  center.  The  whole  an- 
imal may  be  regarded  as  built  up  by  the  joining  of  a  number 
of  essentially  similar  segments.  A  more  minute  examina- 
tion will  show  that 
these  segments  have 
been  materially 
modified  in  some 
portions  of  the  ani- 
mal, but  they  have 
not  been  in  any  re- 
spect organized,  as 
have  the  different 
parts  of  higher  ani- 
mals. This  simple 
animal,  as  has  al- 
ready been  seen,  is 
an  untiring  worker  in 
preparing  and  ferti- 
lizing soil  for  plants, 
and  thus  is  a  most 
efficient  helper  to 


BUTTERFLY  ON  ALFALFA 


Insects.  —  Experi- 
ment 133.  —  Procure  a 

grasshopper  or  honey-bee,  as  a  type  insect,  and  inclose  it  in  a  small, 
glass-covered  box.  Into  how  many  parts  is  the  body  divided? 
Describe  these  parts.  To  which  part  are  the  legs  attached  ?  The 
wings?  How  many  legs  are  there?  How  many  wings?  Notice 
the  largest  part  into  which  the  body  is  divided.  Notice  the  eyes 
and  the  feelers,  or  antennae,  on  the  head.  Write  a  short  descrip- 
tion of  the  general  characteristics  of  the  bee's  body. 


INSECTS 


403 


The  insecte  are  among  the  most  important  of  animals. 
This  class  contains  more  than  half  the  known  animal  species. 
They  are  spread  widely  over  all  parts  of  the  earth. 

Both  good  and  bad  insects  abound.  Economically,  they 
furnish  millions  upon  millions  of  dollars'  worth  of  produce' 
every  year  and  on  the  other  hand  destroy  hundreds  of 
millions  of  dollars'  worth  of  crops  and  trees.  It  has  been 
estimated  that  in  the  United  States  insects  destroy  every 
year  crops  and  trees  which  have  a 
value  of  $50,000,000,  to  say  nothing 
of  the  countless  losses  due  to  dis- 
eases spread  by  flies  and  mosquitoes. 
(Page  452.)  Not  many  years -ago 
grasshoppers  nearly  devastated  sev- 
eral of  the  middle  western  states. 

The  most  productive  insects  are 
the  silkworms  and  the  bees.  With- 
out the  silkworm  (Figure  131)  there 
would  be  no  silk  produced,  and  with- 
out the  bee,  no  honey.  These  two 
products  each  year  run  into  hundreds 

of  millions  of  dollars.    We  have  already  seen  that  bees  and 
other  insects  are  needed  also  for  the  fertilization  of  flowers. 

Among  the  most  interesting  of  the  insects  and  perhaps, 
everything  considered,  the  most  valuable,  is  the  honey-bee. 
This  is  the  great  flower  fertilizer ;  it  would  fertilize  about  all 
the  plants  man  really  needs  except  the  red  clover.  In  the 
United  States  alone  there  is  produced  by  it  about  twenty- 
five  million  dollars'  worth  of  honey  and  wax  each  year. 

In  Experiment  133,  it  was  found  that  the  body  of  the 
bee,  like  other  insects,  is  divided  into  three  parts.  These 
parts  are  called  head,  thorax,  and  abdomen.  The  eyes 


FIGURE  131 


404 


LIFE    ON   THE    EARTH 


and  the  feelers,  or  antennae,  are  on  the  head.  The  mouth 
is  a  very  complex  organ,  fitted  both  for  biting  and  for  suck- 
ing. The  six  legs  and  four  wings  are  on  the  thorax.  The 
hind  leg  of  each  working  bee  is  so  shaped  and  fringed  with 
'hairs  that  it  forms  a  pollen  basket. 

Honey-bees  live  in  large  colonies  and  in  the  colony  there 
are  three  kinds  of  bees,  the  male  bees,  or  drones,  the  workers, 


BEEHIVES 
Hundreds  of  dollars'  worth  of  honey  are  produced  here  each  year. 

and  the  queen  or  female  bee.  The  workers  are  the  ones 
that  make  all  of  the  honey  and  wax,  do  all  the  work  of  the 
hive  and  feed  the  grubs  on  rich  food  formed  in  their  own 
stomachs,  as  well  as  on  pollen  mixed  with  honey.  The 
grubs  are  the  first  stage  in  the  development  of  the  bee 
from  the  egg.  The  queen  lays  all  the  eggs,  sometimes  as 
many  as  a  million.  There  is  but  one  queen  in  each  swarm. 
Whenever  another  queen  is  ready  to  be  hatched,  the  old 


VERTEBRATES 


405 


queen  takes  about  half  the  colony  and  goes  off  to  form 
another  swarm. 

The  wax  is  secreted  from  glands  in  the  abdomens  of  the 
workers  and  with  this  the  bees  build  the  comb.  Each  cell 
is  hexagonal  in  cross  section  and 
the  comb  is  so  constructed  that 
the  least  possible  amount  of  wax 
will  inclose  the  greatest  possible 
amount  of  honey.  The  nectar 
at  the  bases  of  flowers  supplies 
the  bee  with  the  material  from 
which  it  makes  the  honey.  It  is 
in  seeking  for  this  that  the  bee 
visits  so  many  flowers  and  scrapes 
the  pollen  on  to  the  different 
parts  of  its  body  to  be  borne 
away  to  fertilize  other  flowers 
which  it  enters. .  Such  an  inter- 
esting animal  and  so  exceedingly 
useful  is  the  bee  that  hundreds 
of  books  have  been  written  about 
it,  more  than  about  any  other 
domestic  animal.  Some  of  these 
should  be  read  for  further  in- 
formation concerning  this  most 
instructive  animal. 

Vertebrates.  —  Experiment  134. 
—  If  possible,  secure  the  skeleton  of 

some  vertebrate  animal,  preferably  A  HUMAN  SKELETON 

man.      Notice  how  the  bones  are  Notice  how  the  boneg  are 

fitted  to  each  other  and   how  the  ranged  to  protect  thiMii-ii.- 

joints  are  arranged  to  allow  move-  organs. 


406 


LIFE    ON   THE    EARTH 


ment.     Observe  how  carefully  the  brain  and  the  spinal  cord  are 
protected,  and  also  the  thorax,  which  contains  the  heart  and  lungs. 

If  a  human  skeleton  is 
procured,  notice  the  curv- 
ing of  the  spine  which  en- 
ables the  body  to  stand 
erect. 


We  have  just  studied 
briefly  some  of  the  in- 
vertebrates most  closely 
related  to  the  welfare  or 
injury  of  man.  Man 
himself  belongs  to  the 
other  great  class,  verte- 
brates. The  higher  ani- 
mals which  furnish  him 
with  the  greater  part  of 
his  animal  food  also  be- 
long to  this  class.  Al- 
though there  are  great 
variations  in  the  struc- 
ture of  vertebrate  ani- 
mals, yet  they  are  alike 
in  having  a  backbone 
and  an  inner  supporting 
skeleton. 

The  bony  skeleton  in 
the  higher  forms  of  ani- 
mal life  consists  of  a 
vertebral  column,  skull, 
ribs,  and  appendages. 
The  main  skeleton  pro- 


THE  NERVOUS  SYSTEM  OF  MAN 

Notice  how  the  nerves  are  distributed 
to  all  parts  of  the  body. 


BREATHING  407 

tects  the  most  delicate  organs  and  acts  as  a  support  for  the 
attachment  of  the  muscles.  The  appendages,  like  the  legs 
and  arms  in  man,  are  jointed  to  the  central  part  of  the 
skeleton,  and  it  is  the  action  of  the  muscles  in  moving  these 
about  the  joints  that  makes  movement  from  place  to  place 
possible. 

In  the  skull  is  situated  the  great  nerve  center  of  the 
animal,  the  brain,  and  from  this  through  the  vertebral 
column  passes  the  great  nerve  distributor,  the  spinal  cord. 
From  the  brain,  nerves  are  sent  to  all  the  muscles  of  the 
body,  to  the  skin  and  to  those  organs,  like  the  eye  and 
the  ear,  which  transmit  to  the  brain  impressions  received 
from  without  the  body.  These  nerves  give  the  stimuli 
which  cause  the  muscles  to  thicken,  or  contract.  In  fact, 
all  the  voluntary  movements  of  animals  are  controlled  from 
the  brain,  as  the  movements  of  trains  on  a  railroad  are  con- 
trolled from  the  dispatcher's  office. 

Breathing.  —  All  animals  must  have  a  way  to  breathe, 
or  energy  cannot  be  supplied  to  carry  on  the  activities  of 
the  body.  Different  animals  breathe  in  different  ways, 
but  in  the  higher  vertebrates  and  in  man  it  is  the  same. 
Breathing  in  man  will,  therefore,  be  taken  as  the  type. 

Air  enters  the  body  through  the  nose  or  mouth,  and 
passes  down  through  the  windpipe  into  the  lungs.  In  order 
to  keep  out  dust  and  germs,  the  opening  of  the  nose  is 
supplied  with  a  large  number  of  hairs  projecting  from  the 
mucous  membrane  which  lines  the  whole  nasal  chamber. 
These  hairs  and  the  secretion  from  the  membrane  catch  and 
hold  most  of  the  harmful  particles. 

It  is  most  important  that  air  should  be  breathed  through 
the  nose  and  not  through  the  mouth.  Air  which  enters 


408  LIFE    ON   THE    EARTH 

the  lungs  through  the  mouth  is  not  sifted  as  it  is  when  it 
passes  through  the  nose ;  moreover  it  is  not  sufficiently 
warmed  because  the  mouth  passage  is  much  shorter  than 
the  nasal  passages.  Thus  the  throat  and  lungs  are  irritated 
by  mouth-breathing  and  are  more  liable  to  disease. 

Sometimes  abnormal  spongy  growths  called  adenoids 
partly  fill  the  upper  part  of  the  throat.  They  not  only 
obstruct  nose  breathing  but  also  furnish  a  breeding  place 
for  disease  germs.  It  is  a  simple  matter  for  a  surgeon  to 
remove  them ;  and  unless  they  are  removed,  they  may 
result  in  disordered  stomach,  quarrelsome  disposition, 
stunted  growth,  and  even  stupidity.  Most  of  the  cases 
of  adenoids  are  found  in  children.  Children  may  or  may 
not  outgrow  adenoids,  but  some  or  all  of  the  evil  effects 
remain  if  the  trouble  is  long  neglected.  In  the  interest 
of  mental  and  physical  vigor  as  well  as  of  attractiveness 
of  countenance,  the  removal  of  adenoids  ought  never  to 
be  unduly  postponed. 

At  the  back  of  the  mouth  the  windpipe  and  the  throat 
come  together. 

When  food  is  being  swallowed,  the  passage  into  the  wind- 
pipe must  be  closed,  and  this  is  done  by  the  lit.tle  valvelike 
epiglottis.  If,  in  swallowing,  the  epiglottis  is  not  able  to 
close  quickly  enough,  something  may  pass  into  the  wind- 
pipe and  cause  choking.  The  windpipe,  at  the  upper  part 
of  the  chest,  branches  into  two  parts,  one  branch  going  to 
each  of  the  lungs. 

The  lungs  fill  the  upper  part  of  the  chest  and  infold 
the  heart.  In  them  the  air  tubes  divide  again  and  again, 
forming  a  vast  network  of  tubes  which  grow  smaller  and 
smaller  until  they  end  in  little  air  sacks.  Interlacing  with 
these  air  tubes  are  veins  and  arteries  which  carry  the  blood. 


BREATHING 


409 


The  tiniest  parts  into  which  the  blood  vessels  are  divided, 
the  capillaries,  form  close  networks  within  the  linings  of 
the  air  sacks.  The  air  and  blood  are  thus  separated  by  an 
exceedingly  thin  animal  tissue,  which  allows  an  exchange 
of  soluble  materials.  Thus  the  blood  is  able  to  take  up  the 
oxygen  needed  and  to  rid  itself  of  the  carbon  dioxide  and 
other  waste  products  which  it  has  accumulated. 

The  air-tight  thoracic  cavity  in  which  the  heart  and 
lungs  are  situated  is  inclosed  and  protected  by  the  ribs 
and  at  the  lower  part  by 
a  dome-shaped  muscle 
called  the  diaphragm. 
Air  enters  the  lungs 
because  the  muscles  of 
the  chest  pull  the  ribs 
so  that  they  move  up- 
ward and  outward  and 
the  muscles  of  the  dome- 
shaped  diaphragm  cause 
it  to  move  downward. 
These  two  actions  en- 
large the  thoracic  cav- 
ity. The  air  enters  in 

the  same  way  that  it  enters  a  hollow  rubber  ball  that  has 
been  compressed  and  then  set  free.  When  the  ribs  move 
downward  and  the  diaphragm  upward,  the  air  is  expelled  as 
in  the  rubber  ball  when  compressed. 

There  are  then  two  ways  in  which  air  can  be  made  to 
enter  the  lungs,  the  "  raising  of  the  chest  "  and  the  move- 
ment of  the  diaphragm.  In  the  proper  kind  of  breathing 
these  two  movements  go  on  together.  The  lungs  are  filled 
throughout  and  not  simply  at  either  the  top  or  bottom. 


THE  LUNGS 

They  are  here  pulled  aside  to  show 
the  heart. 


410  LIFE    OX    THE    EARTH 

If  this  is  to  be  accomplished,  the  body  must  be  free  and 
not  restricted  by  tight  clothing  about  the  chest  or  the  lower 
part  of  the  trunk  of  the  body,  the  abdomen.  Not  only  is 
the  right  kind  of  breathing  necessary  for  properly  supplying 
the  blood  with  oxygen,  but  also  that  the  lung  tissues  them- 
selves may  be  properly  nourished  and  cared  for.  We 
should  be  particularly  careful  about  this  now  that  infec- 
tious diseases  of  the  lungs  are  so  prevalent. 

Circulation.  —  Experiment  135.  —  If  a  compound  microscope 
can  be  procured,  tie  a  string  tightly  around  the  end  of  a  clean  finger, 
and  when  it  has  become  full  of  blood,  prick  it  quickly  with  a  steri- 
lized needle.  Rub  the  drop  of  blood  that  comes  out  on  a  glass 
slide  and  quickly  examine  under  the  microscope.  Notice  the  great 
number  of  round,  disklike  bodies,  red  corpuscles.  Try  to  find  an 
irregular-shaped  body  which,  while  the  blood  remains  fresh,  slowly 
changes  its  shape,  a  white  corpuscle.  These  are  rather  difficult 
to  find,  but  can  be  seen  if  the  drop  of  blood  is  thoroughly  examined 
quickly  enough. 

In  order  that  all  parts  of  the  body  may  be  provided 

with  the  materials  used  in  building  their  cells  and  in  doing 

o0  the  work  necessary  for  continued 

<P%  o^     o§  existence  there  must  be  a  dis- 

°°  °o  °^rv  b°°  o°°o  o  °oQ   tributorv  svstem.     This  is  neces- 

0°°      00  $<3  nO  O      °OQ       cP    o 

o   °@8>0°o  O°OQ  °0°c0oQ     sary  wherever  diversified  work 

<$>    °  o°o°^°£°££f°       is  to  be  carried  on-     T1"8  neces- 
o%°®  o°°%°  !f  9°      sity  has  brought  into  effect  the 

railway  and  canal  systems  of  the 

°  world.    The  body  is  a  little  world 

FIGURE  132  ,      .,      ,,         j  •     i 

by  itself,  and  it  has  a  most  com- 
plete and  wonderfully  adapted  system  for  supplying  the 
material  needed  and  for  removing  the  waste.  The  center 
and  motive  power  of  this  system  is  the  heart.  The  medium 
of  circulation  is  the  blood. 


CIRCULATION  411 

When  the  blood  is  examined,  it  is  found  to  consist  of  a 
watery  liquid,  called  the  plasma,  a  great  number  of  little 
disk-shaped  bodies,  the  red  corpuscles,  and  some  irregular 
whitish  bodies,  the  white  corpuscles  (Figure  132). 

The  white  corpuscles  are  protoplasmic  cells  possessing 
the  power  of  movement  and  even  of  working  their  way  out 
of  the  blood  vessels.     They  are  the  soldiers  of  defense  of 
the  human  body.     When  a  white  corpuscle  comes  in  contact 
with  a  disease  germ,  the  body  of  the  corpuscle  takes  the 
germ  into  it  and  tries  to  digest  it.     The  germ  in  turn  tries 
to  multiply  inside  the  corpuscle  and  to  feed  on  it.     Unless 
the  germs  increase  in  number  too  rapidly, 
the  white  corpuscles  come  off   victorious.          v-^  / 
The  blood  also  provides  other  substances        ^  f~^^ 
that  are  probably  even  more  important  than  v    . .)  \ 

white  corpuscles  in  fighting  disease.     Some  \^ 

of  these  substances  kill  disease  germs  and  A  WHITE  CORPUS- 
others  counteract  germ  poisons.  CLE  DIGESTING  A 

mi  f          •  PI  GERM     (Greatly 

Ihe  mam  function  or  the  red  corpuscles      magnified.) 

is  to  carry  oxygen  from  the  lungs  to  the 
different  living  cells  of  the  body.  They  contain  a  pigment, 
haemoglobin,  which  carries  the  oxygen  and  gives  the  blood 
its  color.  The  plasma,  an  exceedingly  complex  fluid,  is 
composed  largely  of  water,  but  contains  the  nutrient  and 
waste  materials  supplied  by  the  different  organs  of  the  body. 
The  blood  passes  through  different  kinds  of  vessels. 
Those  leading  from  the  heart  are  called  arteries,  and  those 
returning  to  the  heart  are  called  veins.  As  the  arteries 
proceed  from  the  heart  they  divide  continually,  becoming 
smaller  and  smaller  until  they  terminate  in  very  small, 
thin-walled  vessels  called  capillaries.  These  capillaries 
unite  and  form  veins.  Thus  the  blood  is  continually  flow- 


412 


LIFE    ON   THE    EARTH 


ing  from  the  heart  through  the  arteries  and  capillaries  into 
the  veins  and  back  to  the  heart. 

As  a  rule  the  arteries  are  below  the  surface  of  the  body, 
where  they  are  protected,  but  if  the  finger  is  placed   on 

the  wrist  or  the  side  of 
the  face  near  the  ear, 
an  artery  can  be  felt 
through  which  the  blood 
is  pulsing.  The  veins 
can  be  seen  in  the  back 
of  the  hand  and  a  pin 
piercing  the  body  any- 
where will  break  open 
some  of  the  capillaries 
and  cause  blood  to  ooze 
out.  The  capillaries 
spread  throughout  the 
entire  tissue  of  the  body 
and  supply  with  food 
and  oxygen  the  different 
living  cells  of  which  the 
body  is  composed. 

The  heart  is  a  muscu- 
lar force  pump  composed 
of  four  chambers,  two 
auricles  and  two  ven- 
tricles. It  is  shaped 
somewhat  like  a  pear  and  is  situated  almost  directly  be- 
hind the  breastbone.  The  blood  coming  back  from  the 
veins  flows  into  the  right  auricle,  a  chamber  with  rather 
flabby  walls.  From  here,  it  passes  through  a  valve  into 
the  right  ventricle,  which  is  a  chamber  with  very  thick 


THE  CIRCULATORY  SYSTEM 

Notice  the  veins  (white)  are  nearer  the 
surface  than  the  arteries  (black). 


THE  SENSES  413 

muscular  walls.  From  the  right  ventricle,  the  blood  is 
driven  out  through  the  arteries,  capillaries,  and  veins  of 
the  lungs,  where  carbon  dioxide  is  given  off  and  oxygen 
absorbed  by  the  red  corpuscles. 

Returning  from  the  lungs,  the  blood  enters  the  left  auricle 
and  when  this  Becomes  full,  passes  through  a  valve  into 
the  left  ventricle.  This  has  such  powerfully  muscular  walls 
that  it  is  able  to  force  the  blood  through- 
out the  body  and  back  again  to  the 
right  auricle.  As  the  blood  leaves  either 
ventricle,  there  are  valves  that  close  and 
prevent  its  return.  If  the  hand  is  placed 
a  little  to  the  left  of  the  breastbone,  the 
strong  contraction  of  the  ventricle  can 
be  felt. 

CROSS  SECTION  OF 
THE  HUMAN  HEART 

The  Senses.  -  In  order  that  the  brain  Showing  auride  _ 
may  communicate  with  the  outside  world  tricle,  and  ventricle 
and  so  be  able  to  protect  the  animal 
from  destruction  and  to  provide  for  its  well-being,  animals 
are  provided  with  a  number  of  sense  organs  which  com- 
municate with  the  brain  by  the  nerves.  The  most  con- 
spicuous sensations  of  the  human  body  are  taste,  smejl, 
touch,  sight,  and  hearing. 

On  the  tongue  and  in  the  nose  are  cells  which  transmit  to 
the  brain  the  impressions  produced  upon  them  by  different 
qualities,  the  one  of  solutions  and  the  other  of  gases.  The 
sensations  thus-  produced  are  called  taste  and  smell. 

The  sensation  of  touch  originates  in  the  skin  and  is  much 
more  acute  in  some  portions  than  in  others.  The  tips  of 
the  fingers  in  the  blind  are  often  trained  to  such  delicate 
perception  that  they,  in  a  great  degree,  take  the  place  of 


414  LIFE    ON   THE    EARTH 

the  lacking  sense  organ.  These  sensations,  like  all  others, 
are  carried  to  the  brain  by  the  nerves  and  there  interpreted 
into  the  sensation  of  touch. 

Sight.  —  The  organ  of  sight,  the  eye,  is  an  exceedingly 
sensitive,  automatically  adjustable  camera  that  records 
through  the  nerves.  The  camera  box  is  the  hard,  bony 
socket  in  which  the  eye  is  placed,  the  eyelid  is  the  shutter, 
and  the  iris,  the  diaphragm.  The  iris  is  the  membrane  in 

the  front  of  the  eye  which 
opens  or  contracts  to  let 
in  more  or  less  light.  In 
the  center  of  it  is  a  hole, 
the  pupil. 

Back  of  the  diaphragm, 
or  iris,  is  a  small  adjust- 
able lens  and  beyond  this 
the    sensitive    plate,    the 
CROSS  SECTION  OF  THE  HUMAN  EYE     retina.     Between  the  iris 

The  pupil  is  the  opening  surrounded        and    the    front    of    the   eve 
by  the  iris.  .  ,.,  .      •    i 

is  a  waterylike  material, 

the  aqueous  humor,  which  keeps  the  front  of  the  eye  ex- 
tended into  its  rounded  form.  Back  of  the  lens  is  a  thick, 
transparent,  jellylike  material,  the  vitreous  humor,  which 
holds  the  retina  extended  and  keeps  the  eye  from  collapsing. 
Instead  of  moving  the  retina  back  and  forth  to  focus  a 
picture,  as  is  done  with  the  ground-glass  plate  in  a  camera, 
the  eye  lens  is  capable  of  adjusting  itself  so  as  to  focus  objects 
which  are  at  different  distances.  Leading  back  to  the  brain 
from  the  retina  is  the  optic  nerve,  which  carries  the  impres- 
sions made  on  the  retina  to  the  brain,  where  they  are  inter- 
preted into  the  sensation  of  sight. 


SIGHT 


415 


MOVING  PICTURE  OF  A  HIOH  JUMP 


416  LIFE    ON   THE    EARTH 

This  rough  comparison  is  by  no  means  a  description  of 
the  eye,  for  it  is  a  most  complex  and  wonderful  organ,  vastly 
superior  in  construction  to  a  camera.  A  technical  descrip- 
tion would,  however,  be  out  of  place  here.  The  impres- 
sion made  on  the  retina  remains  for  an  instant ;  and  so  if 
successive  pictures  (about  twelve  a  second)  are  taken  of  a 
moving  object  and  projected  on  a  screen  at  the  same  rate 
the  eye  will  not  distinguish  the  intervals  between  the  pic- 
tures and  the  object  will  appear  to  be  in  motion.  This  is 
the  way  in  which  moving  pictures  are  produced. 

Sometimes  the  lens  is  not  able  to  focus  a  picture  distinctly 
on  the  retina,  and  then  it  is  necessary  to  aid  the  lens  of  the 
eye  with  artificial  lenses,  or  glasses.  Silly  notions  about 
one's  personal  appearance  in  glasses  should  never  stand  in 
the  way  of  wearing  glasses  when  they  are  necessary.  If 
there  is  a  strained  feeling  when  the  eyes  are  used,  or  if 
headaches  result  from  continued  use  of  the  eyes,  reliable 
advice  should  be  sought. 

The  eye  is  so  important  for  our  usefulness  and  happiness 
that  the  greatest  care  should  be  taken  of  it.  One  should 
not  read  when  he  is  lying  on  his  back,  when  the  light  is 
either  poor  or  glaring,  or  when  the  book  cannot 
be  held  steadily.  The  eye  may  be  infected  from 
public  washbowls,  public  towels,  or  even  by 
rubbing  with  one's  own  fingers.  Any  infection 
of  the  eye  demands  skillful  treatment  and  should 
not  be  trifled  with. 


FIGURE  133  Sound  and  Hearing.  —  Experiment  136.  —  Arrange 
a  large,  wide-mouthed  bottle  with  a  small  bell  sus- 
pended in  it  from  the  stopper  and  a  delivery  tube  extending  through 
the  stopper.  (Figure  133.)  Attach  the  delivery  tube  by  a  thick- 
walled  rubber  tube  to  an  air  pump  and  exhaust  the  air  from  the 


SOUND  AND   HEARING  417 

bottle.  Shake  the  bottle  so  that  the  bell  can  be  seen  to  ring  but 
does  not  strike  the  sides  of  the  bottle.  Can  the  sound  be  heard 
distinctly? 

Experiment  137.  —  Suspend  a  pith  ball  by  a  light  thread  so  that 
it  may  swing  freely.  Strike  a  tuning  fork  and  quickly  place  it  in 
very  light  contact  with  the  pith  ball.  The  ball  will  be  set  in  mo- 
tion by  the  vibrations  of  the  tuning  fork. 

In  Experiment  136  it  was  found  that  if  the  air  was  ex- 
hausted and  the  bell  did  not  touch  the  sides  of  the  bottle, 
almost  no  sound  was  heard  when  the  clapper  of  the  bell 
showed  that  the  bell  was  ringing.  This  shows  that  the  sounds 
we  usually  hear  are  transmitted  in  some  way  by  the  aid  of 
the  air.  In  Experiment  137  the  sounding 
body  was  seen  to  be  vibrating.  Since 
these  vibrations  set  the  pith  ball  moving, 
we  may  understand  that  the  air  surround- 
ing the  tuning  fork  must  also  have  been 
set  in  motion. 

Sound  has  been  found  to  be  a  wave 

motion    in    a    material    medium.      If    a 

.    .  ,  i     j?       i          i  FIGURE  134 

scratch  is  made  on  the  end  of  a  long  log, 

it  can  be  heard  if  the  ear  is  placed  at  the  other  end  of  the 
log,  when  it  cannot  be  heard  if  the  ear  is  away  from  the  log. 
In  this  case  the  medium  is  the  wood. 

If  a  stone  is  dropped  into  a  quiet  pond,  the  rippling  waves 
developed  will  extend  often  to  the  farthest  shore  of  the  pond, 
but  a  chip  floating  near  where  the  stone  fell  will  not  be  im  >vo  1 
from  its  position  except  up  and  down.  Thus  the  waves 
traveled  outward  from  the  point  of  origin,  but  there  was  IK. 
outward  movement  of  the  water.  If  a  long  rope,  attached 
at  one  end  and  held  in  a  horizontal  position,  is  suddenly 
struck  with  a  stick,  a  wave  motion  will  travel  along  the 


418 


LIFE    ON   THE    EARTH 


rope  from  end  to  end,  but  the  particles  of  the  rope  will 
simply  move  up  and  down.  It  is  in  a  similar  way  to  this 
that  the  sound  waves  travel,  but  the  particles  which  trans- 
mit the  sound  only  move  back  and  forth  through  small 
distances.  (Figure  134.)  An  echo  is  simply  a  reflection  of 
sound  waves  from  some  obstruction  they  meet. 

The  ear,  which  is  the  sound  transmitter  of  the  body;  con- 
sists of  the  outer  ear,  which  is  so  arranged  as  to  catch  the 

sound  waves  and  converge 
them  upon  the  ear  drum. 
The  ear  drum  is  a  thin 
membrane  stretched  tightly 
across  a  bony  opening  and 
vibrates  when  the  air  waves 
strike  it,  as  a  drum  does 
when  struck  by  the  drum- 
stick. On  its  inner  side 
the  drum  is  attached  to  the 
inner  ear  by  a  chain  of 
three  bones.  The  sensitive 
cells  of  the  inner  ear  trans- 
mit the  impressions  made  by  the  sound  vibrations  through 
the  auditory  nerve  to  the  brain,  where  they  are  interpreted 
into  the  sensation  of  sound. 

The  drum  head  of  the  ear  is  easily  broken,  and  therefore 
no  hard  instrument  should  ever  be  thrust  into  the  ear. 
There  is  an  old  saying  that  one  should  never  pick  his  ear 
with  any  kind  of  hard  instrument  having  a  smaller  point 
than  one's  elbow.  Immediate  and  skillful  attention  should 
be  given  to  any  inflammation  of  the  ear.  If  neglected  it 
may  lead  to  deafness  or  even  to  an  exceedingly  dangerous 
abscess  in  the  bone  back  of  the  ear. 


CROSS  SECTION  OF  THE  HUMAN  EAR 


FOOD  419 

Food.  —  Experiment  138.  —  Chop  a  piece  of  the  white  of  a  hard- 
boiled  egg  into  pieces  about  as  large  as  the  head  of  a  pin  and  place 
in  a  test  tube.  Chop  up  another  piece  much  finer  than  this  and 
place  it  in  a  second  test  tube.  Make  a  mixture  of  100  cc.  of  water, 
5  cc.  of  essence  of  pepsin,  and  2  cc.  of  hydrochloric  acid.  Pour  into 
each  test  tube  enough  of  this  mixture  to  cover  the  white  of  egg  to 
a  considerable  depth.  Shake  thoroughly  and  put  in  a  place  where 
the  temperature  can  be  maintained  at  37°  C.  or  98°  F.  A  fireless 
cooker  or  a  bucket  of  warm  water  is  good  for  this.  Allow  to  stand 
for  several  hours,  keeping  the  temperature  constant.  The  white 
of  egg  is  dissolved,  the  action  being  more  rapid  in  the  second  tube. 
Try  the  same  experiment  using  water;  using  dilute  hydrochloric 
acid.  Do  these  have  the  same  effect  as  when  used  with  the  pepsin  ? 
The  pepsin  solution  is  an  artificial  gastric  juice. 

In  order  that  the  work  of  the  body  may  be  carried  on, 
food  is  required.  This  food  may  be.  supplied  by  either 
animals  or  plants.  The  original  source  of  all  animal  and 
plant  food,  as  has  been  seen,  is  in  the  chlorophyll  manu- 
factory of  the  leaf  and  green  stem.  After  this  leaf  food 
has  been  manufactured,  it  is  simply  modified  by  the  plants 
and  animals  through  which  it  passes.  The  food  is  used 
(1)  in  growing  new  cells,  (2)  in  repairing  cells  that  have 
been  used  up  or  destroyed,  (3)  in  providing  energy  to  cam- 
on  the  activities  of  the  body  and  maintain  its  heat,  or  (4)  in 
doing  external  work,  such  as  moving  the  body  itself  from 
place  to  place  or  moving  other  bodies. 

To  furnish  any  of  this  energy,  the  cells  must  be  able  to 
combine  food  with  oxygen.  To  do  this  the  food  must  be 
digested  or  prepared  so  that  it  can  pass  through  animal 
tissue.  In  the  higher  animals,  a  complicated  apparatus  is 
provided  to  accomplish  this.  In  man  it  is  briefly  as  follows : 
a  long,  continuous  tube,  the  food-tract  or  the  alimentary 
canal  (Figure  135)  extends  through  the  body.  Different 


420 


LIFE    ON   THE    EARTH 


portions  of  this  tube  are  adapted  to  different  processes.  In 
the  mouth,  the  teeth  grind  the  food  into  small  bits  and  mix 
it  with  the  saliva.  This  is  an  exceedingly  important  part 
of  the  process,  because  if, the  food  is  not  ground  fine,  the 
digestive  juices  cannot  readily  get  at  it,  and  the  whole  process 
of  digestion  is  greatly  retarded.  Thus  much  more  energy  is 

expended  than  otherwise 
would  be.  The  saliva  is 
necessary  to  digest  some  of 
the  starch  and  to  aid  in  the 
further  digestion. 

The  food  passes  from 
the  mouth  down  the  throat 
and  through  an  orifice  to 
the  stomach.  This  is  a 
large  pouch  which  will  hold 
usually  from  three  to  four 
pints.  It  has  muscular 
walls  which  enable  it  to 
contract  and  expand,  thus 
keeping  the  food  mov- 
ing about  so  that  it  is 
thoroughly  mixed  with  the 
gastric  juice.  The  gastric 
juice  is  secreted  by  little 
glands  thickly  embedded 
in  the  lining  of  the  stomach.  Artificial  gastric  juice  was 
made  in  Experiment  138.  Some  of  the  proteins  (foods  con- 
taining nitrogen)  are  digested  in  the  stomach,  although  the 
larger  part  of  digestion  takes  place  in  the  small  intestine. 

From  the  stomach  the  food  passes  through  a  valve  into 
the  small  intestine.    This  is  a  complexly  coiled  tube  which 


FIGURE  135 


SUMMARY  421 

fills  the  larger  part  of  the  abdomen.  The  inner  wall  of 
the  tube  is  lined  with  glands  which  secrete  digestive  juices, 
and  into  the  intestine  are  poured  the  secretions  from  two 
large  glands,  the  pancreas  and  the  liver.  The  small  intes- 
tine is  the  great  digestive  organ  of  the  body.  Here  the  fats 
and  oils  are  digested,  and  the  digestion  of  the  starches  and 
proteins  is  completed.  The  small  intestine  opens  through  a 
valve  into  the  large  intestine,  a  tube  five  or  six  feet  long 
decreasing  in  size  toward  the  exit  from  the  body.  There 
is  little  digestion  in  the  large  intestine. 

The  changes  that  take  place  in  the  food  as  it  passes 
through  the  alimentary  canal  are  very  complex,  but  dur- 
ing its  progress  the  valuable  part  of  the  food  is  so  changed 
and  prepared  that  it  can  be  absorbed  by  the  blood  and 
transported  by  it  to  the  different  parts  of  the  body  where 
its  energy  is  needed.  Absorption  takes  place  all  along 
the  alimentary  canal  wherever  the  food  has  been  suffi- 
ciently prepared. 

In  the  entire  process  of  digestion  of  food  the  only  part 
that  can  be  controlled  by  the  individual  is  the  chewing  of 
the  food.  It  is  necessary  that  the  food  be  ground  fine  in 
order  that  the  digestive  juices  may  readily  act  upon  it  and 
not  leave  any  undigested  fragments  as  abiding  places  for 
germs.  Decayed  and  unbrushed  teeth  furnish  unlimited 
breeding  places  for  germs.  Careful  experiments  have  shown 
that  the  health  of  the  body  and  the  mental  vigor  are  greatly 
increased  by  properly  caring  for  the  teeth.  The  teeth  must 
be  kept  clean  and  all  cavities  must  be  properly  filled  if  health 

is  to  be  maintained. 

SUMMARY 

Plants  and  animals  make  up  the  live  part  of  the  earth. 
Most  green  plants  consist  of  root,  stem,  and  leaves.  The  root 


422  LIFE    ON    THE    EARTH 

anchors  the  plant  to  the  ground  and  takes  in  from  the  soil 
all  the  plant's  food  except  carbon.  This  is  supplied  from 
the  carbon  dioxide  of  the  air,  which  enters  the  plant  through 
the  leaves.  Leaves  are  the  original  food  manufactories  for 
all  plants  and  animals.  Stems  vary  greatly  in  the  positions 
they  assume,  but  their  chief  functions  are  to  support  the 
leaves  and  to  conduct  food  solutions  from  the  root  to  the 
upper-structure  of  the  plant.  The  two  great  classes  of 
stems  are  monocotyledonous  and  dicotyledonous. 

The  stem  also  usually  supports  the  flower,  which  consists 
in  the  main  of  calyx,  corolla,  stamen,  and  pistils.  The  chief 
function  of  the  flower  is  to  produce  the  seeds  from  which 
succeeding  generations  of  plants  grow.  The  enlarged  tip  of 
the  stamen  is  called  the  anther.  This  produces  pollen 
grains.  When  a  pollen  grain  of  the  right  sort  falls  on  the 
head  of  the  pistil,  called  the  stigma,  it  fertilizes  an  egg  cell 
in  the  ovary,  wThich  is  at  the  base  of  the  pistil,  thus  produc- 
ing the  embryo  of  a  new  plant,  which  is  the  living  part  of  a 
seed.  Pollen  grains  are  carried  and  spread  by  the  wind  and 
by  insects  and  birds.  The  seeds  are  also  scattered  by  the 
wind,  by  animals,  and  by  flowing  streams. 

Besides  these  green  plants  which  prepare  their  own  foods, 
there  is  another  great  group  of  plants  that  may  be  called 
dependent.  Instead  of  preparing  their  own  food  by  the 
help  of  the  sun,  they  live  upon  food  that  has  been  prepared 
by  green  plants. 

Among  the  familiar  dependent  plants  are  mushrooms  and 
toadstools.  Bacteria  arid  yeasts  are  single-celled  dependent 
plants.  A  bacterium  reproduces  by  dividing  in  two.  A 
yeast  reproduces  by  budding.  Molds  are  dependent  plants 
which  are  made  up  of  many  cells  and  which  reproduce  by 
spores. 


QUESTIONS  423 

Animals  take  their  energy  indirectly  from  the  foods  pre- 
pared by  green  plants  or  by  other  animals.  They  are 
usually  classed  as  invertebrate  and  vertebrate.  The  lowest 
form  of  invertebrate  is  the  protozoon.  Worms  and  insects 
are  other  forms  of  invertebrates,  the  importance  of  which  is 
seldom  realized. 

The  bony  skeleton  in  the  higher  forms  of  vertebrates 
consists  of  a  backbone,  skull,  ribs,  and  appendages.  In  the 
skull  is  the  brain,  connected  with  the  various  parts  of  the 
body  by  nerves.  Vertebrates  breathe  by  receiving  air 
through  the  windpipe  into  the  lungs.  This  is  done  by  the 
muscles  of  the  chest  and  the  diaphragm.  The  lungs  purify 
the  blood,  which  circulates  from  the  heart  through  the 
arteries  and  capillaries  and  returns  through  the  veins. 

The  five  senses  are  taste,  smell,  touch,  sight,  and  hearing. 
These  sensations  are  carried  to  the  brain  by  the  nerves, 
which  come  from  the  nose,  the  mouth,  the  skin,  the  eye,  and 
the  ear,  respectively.  Sound  is  a  wave  motion  in  a  material 
medium.  The  ear  is  a  sound  transmitter,  which  conveys 
sound  vibrations  by  way  of  the  auditory  nerve  to  the  brain. 

For  all  the  activities  of  body  and  brain  food  is  required. 
As  the  food  passes  through  the  alimentary  canal,  various 
juices  are  mixed  with  it  and  certain  parts  of  it  are  digested 
and  absorbed  into  the  circulatory  system  of  the  body. 

QUESTIONS 

What  are  the  three  parts  into  which  many  plants  can  be  readily 
separated? 

In  what  three  respects  are  plants  and  animals  alike? 

Of  what  use  to  the  plant  are  the  roots  ?  Why  are  roots  necessary 
to  the  higher  plants  ? 

Describe  some  different  kinds  of  stems  that  you  have  seen  and 
explain  their  adaptability  or  lack  of  adaptability  for  making 
the  best  of  the  conditions  where  they  were. 


424  LIFE   ON  THE   EARTH 

What  do  the  leaves  do  for  the  plant?     How  do  they  do  it? 

What  is  the  value  to  the  plant  of  the  flower  ?  How  are  the  flowers 
prepared  to  carry  out  their  part  in  the  life  struggle  of  the  plant? 

Describe  any  way  in  which  you  know  that  animals  have  been  of 
assistance  to  plants. 

How  do  plants  provide  for  the  dispersal  of  their  seeds? 

How  does  the  seed  develop  into  a  plant? 

With  what  useful  or  what  harmful  chlorophyll-lacking  plants 
have  you  ever  had  experience? 

Name  and  describe  some  of  the  invertebrate  animals  you  know. 

What  is  the  general  structure  of  the  worm  ? 

What  insects  have  you  known  that  are  beneficial?  What  that 
are  harmful? 

What  is  the  use  to  the  vertebrate  of  the  skeleton  and  the  nervous 
system  ? 

Describe  how  vertebrate  animals  breathe.  Why  is  it  vitally 
necessary  for  them  to  breathe  freely? 

What  is  the  use  of  the  blood?  How  does  it  get  around  to  where 
it  is  needed? 

Describe  the  ways  in  which  man  becomes  aware  of  what  is 
outside  his  body. 

Why  is  food  needed?     How  and  where  is  it  digested? 


CHAPTER  XIV 


rogen 


MAN'S  EXISTENCE  AS  BELATED  TO  PLANT  AND 
ANIMAL  LIFE.     FOODS. 

Fundamental  Foods.  —  The  elements  which  enter  into 
the  structure  of  the  human  body,  such  as  oxygen,  hydrogen, 
nitrogen,  carbon,  etc.,  are  comparatively  few  and  are  abun- 
dant in  the  world  about  us,  either  separately  or  in  compounds. 
But  with  all  of  man's  ingenuity,  he  has  never  learned  to 
manufacture  these  ele- 
ments into  compounds 
that  will  serve  as  food  for 
the  human  body. 

The  leaves  of  plants 
are  the  fundamental  food 
factories  of  the  world. 
Here  carbon,  hydrogen, 
and  oxygen  are  united  by 
the  aid  of  the  sun  into 
plant  foods  called  carbohy- 

j      .  r    ,  ,  ,    •        PROPORTIONS  OF  ELEMENTS  IN  COMPOSI- 

drates.    Fats  and  proteins  TION  OF  LIVINQ  THINGS 

are    two   other    kinds  of 

foods  that  are  also  manufactured  in  the  bodies  of  both 
plants  and  animals,  but  the  carbohydrates  are  the  original 
material  out  of  which  the  living  organism,  whether  plant 
or  animal,  first  produces  fats  and  proteins. 

Air,  water,  and  salt  are  necessary  to  the  processes  of  life, 
425 


426  FOODS 

but  they  are  not  generally  classed  as  foods.  In  leaves 
then  and  in  leaves  only  are  the  lifeless  (inorganic)  sub- 
stances of  the  earth  combined  into  substances  that  will 
support  life  (organic  compounds) .  The  factories  of  nature 
are  open  to  man,  and  he  knows  fairly  well  what  these  fac- 
tories produce.  But  how  the  compounds  are  produced 
either  in  the  plant  or  in  the  animal  and  how  the  active 
material  of  the  living  cells  called  protoplasm  does  its  work 
are  mysteries  to  him.  By  careful  study,  however,  man 
has  learned  a  great  deal  as  to  foods  necessary  to  the  growth 
and  health  of  the  human  body. 

Necessary  Foods.  —  Experiment  139.  —  Place  in  different  test 
tubes  small  amounts  of  (1)  corn  starch,  (2)  grape  sugar,  (3)  scrap- 
ings from  a  raw  potato,  (4)  flour,  and  (5)  the  white  of  an  egg. 
Pour  in  a  little  water  and  shake  thoroughly.  Drop  into  each 
tube  a  few  drops  of  the  iodine  solution  prepared  in  Experiment  120. 

Experiment  140.  —  Place  in  test  tubes  small  quantities  of  (1)  the 
white  of  a  hard-boiled  egg,  (2)  tallow  or  lard,  (3)  grape  sugar,  and 
(4)  any  other  food  which  may  be  handy.  Pour  a  little  concen- 
trated nitric  acid  into  each  tube  and  allow  to  stand  for  a  minute. 
Be  careful  not  to  get  the  nitric  acid  on  the  clothes  or  hands.  Pour 
the  acid  out  into  a  slop  jar  and  wash  the  substances  with  a  little 
water.  Pour  off  the  wash  water  and  pour  on  a  little  strong  am- 
monia. If  the  substances  turn  a  yellow  or  orange  color,  proteins 
are  present.  Which  substances  contain  proteins? 

Experiment  141.  —  Gasoline  vapor  is  very  inflammable ;  be  sure 
in  this  experiment  that  there  is  no  flame  in  the  room.  Place  about 
a  spoonful  of  (1)  both  the  white  and  the  yellow  of  an  egg,  (2)  flax- 
seed  meal,  (3)  yellow  corn  meal,  (4)  white  flour,  and  (5)  other 
foods  it  is  desired  to  test  in  separate  evaporating  dishes  or  beakers 
near  an  open  window.  Pour  on  these  more  than  enough  gasoline 
to  cover  them,  and  stir  thoroughly.  Cover  the  evaporating 
dishes  and  allow  to  stand  for  ten  or  fifteen  minutes.  Pour  the 
gasoline  off  into  a  beaker  and  set  the  beaker  outside  the  window 
until  the  gasoline  has  evaporated.  If  there  is  anything  left  it 


NECESSARY   FOODS 


427 


raust  have  been  dissolved  from  the  food.  If  a  substance  remains, 
place  a  drop  of  it  on  a  piece  of  paper.  Smell  of  it.  Try  to  mix  it 
with  water.  Rub  it  between  the  fingers.  Try  any  other  fat  or 
oil  test  of  which  you  can  think. 

Experiment  142.  —  In  a  place  where  there  is  a  good  draft  so  that 
odors  will  not  penetrate  the  room,  burn  in  an  iron  spoon  over  a 
Bunsen  burner  (1)  small 
pieces  of  meat,  (2)  a 
little  condensed  milk  or 
milk  powder,  (3)  part  of 
an  egg,  and  (4)  any  other 
food.  Is  there  a  residue 
left  after  burning?  If 
so,  this  is  mineral  matter. 

In  the  preceding 
experiments  we  have 
dealt  with  the  three 
great  groups  of  organic 
compounds,  carbohy- 
drates (starches  and 
sugars),  fats  and  oils, 
and  proteins  (foods 
containing  nitrogen) . 
The  foods  that  con- 
tain large  percentages 
of  carbohydrates  are 
vegetables,  fruits,  and 
most  cereals.  The  fats 
are  most  abundant  in  butter,  cream,  fat  meats,  nuts,  choco- 
late, and  vegetable  oils  such  as  olive  and  cottonseed  oils. 
The  common  foods  that  are  rich  in  proteins  are  lean  meats, 
eggs,  beans,  peas,  and  certain  cereals,  especially  oatmeal. 
Milk  contains  all  three  of  these  compounds  in  approximately 
the  proportions  needed  by  the  body. 


A  DATE  PALM 


428 


FOODS 


Careful  experiment  has  shown  that  the  average,  full- 
grown  American  needs  each  day  two  to  three  ounces  of 
proteins,  about  four  ounces  of  fats,  and  a  pound  of  carbo- 
hydrates. The  weight  of  food  eaten,  however,  is  very 
much  greater  than  this,  as  all  foods  are  composed  largely  of 
water,  and  contain  other  substances  which  the  body  throws 

off  as  waste.  The  pro- 
teins are  needed  for 
growth  and  repair,  since 
the  living  part  of  the 
cells,  the  protoplasm,  is 
composed  of  proteins. 

All  foods  furnish 
energy  when  they  are 
oxidized  in  the  body. 
Until  recently  it  was 
thought  that  a  great  deal 
of  meat  was  necessary  to 
furnish  the  energy  re- 
quired for  hard  muscular 
work.  But  investigation 
has  shown  that  this 
energy  can  better  be  sup- 
plied by  carbohydrates 
and  fats.  When  carbo- 
hydrates and  fats  are 

oxidized  in  the  body  to  produce  energy,  the  waste  is  largely 
water  aiyi  carbon  dioxide,  which  the  body  readily  throws  off. 
But  when  for  lack  of  carbohydrates  the  body  is  compelled  to 
oxidize  proteins  to  produce  energy,  certain  nitrogen  wastes 
are  produced  which  the  body  does  not  throw  off  so  easily. 
Continued  strain  of  throwing  off  these  poisonous  wastes  in 


A  BUNCH  OF  DATES 
An  excellent  food  for  hot  climates. 


NECESSARY   FOODS 


429 


large  amounts  may  lead  to  serious  disease.  The  wide- 
spread custom  in  America  of  eating  meat  three  times  a 
day  is  not  only  expensive  but  also  unhealthful.  A  small 
amount  of  meat  once  a  day  is  all  that  even  a  hard-working 
man  needs. 

Where  men  live  in  cold  regions  or  are  much  exposed  to 
cold,  the  body  requires  great  energy  to  keep  up  its  heat. 


SUGAR  CANE  CUTTING 

Fats  are  the  substances  that  oxidize  most  readily  in  the 
human  body,  and  these  are  needed  in  great  abundance  by 
men  who  have  to  withstand  exposure  to  cold.  "  Fats  are 
fuels  for  fighters"  was  a  slogan  of  literal  truth  which  the 
United  States  Food  Commission  used  on  its  posters  during 
the  World  War.  The  body  readily  converts  sugars  into 
energy,  and  so  sugars  are  also  a  valuable  cold  weather  food. 
The  staple  food  of  northern  Africa  is  the  date,  which  is 


430  FOODS 

admirable  for  hot  climates  because  it  is  practically  a  com- 
plete food  with  a  minimum  of  fats. 

Mineral  matter  such  as  iron  for  the  red  corpuscles,  lime 
for  the  bones  and  teeth,  and  phosphorus  for  the  protoplasm 
must  also  be  included  in  our  food.  Eggs  furnish  all  three 
of  these;  milk  is  rich  in  lime;  but  vegetables  and  the 
outer  layers  of  grains  contain  the  main  supplies  of  these 


BANANA  PLANTS 
The  bananas  grow  from  the  top  of  the  plant  in  great  clusters. 

minerals,  since  vegetable  foods  are  more  abundant  elements 
of  diet  with  most  people  than  either  milk  or  eggs. 

Recently  other  substances  called  vitamins  have  been 
found  necessary  to  the  maintenance  of  a  healthy  body. 
They  are  found  in  fresh  (not  salt)  meats,  fresh  milk,  raw 
vegetables  and  fruits,  and  in  the  outer  layers  of  grains. 
Since  heat  drives  off  these  vitamins,  we  must  rely  mainly 


NECESSARY  FOODS  431 

upon  raw  fruits  and  raw  vegetables  for  our  supply  of  these 
substances.  Even  the  slight  heat  necessary  to  pasteurize 
milk  drives  off  the  vitamins. 

A  study  of  the  few  facts  that  have  been  presented 
here  will  indicate  that  vegetables  and  fruit  should  form  a 
much  larger  proportion  of  the  American  diet  than  they  now 
do.  Men  who  live  almost  exclusively  on  white  bread  and 
meat  are  starving  their  bodies  for  certain  very  necessary 
substances,  and  are  overworking  their  systems  to  throw 
off  poisonous  wastes.  When  the  Food  Commission  asked 
during  the  World  War  that  we  eat  less  meat  and  more  of 
the  dark  breads  containing  the  outer  layers,  or  brans,  of  the 
cereals,  they  were  asking  us  to  do  ourselves  as  well  as  our 
soldiers  and  the  Allied  peoples  a  favor. 

Besides  the  necessary  foods,  most  individuals  desire 
especial  additions  for  relishes  and  beverages.  These  com- 
monly consist  of  spices,  tea  and  coffee,  and  other  like  ma- 
terials. When  used  in  moderation,  they  are  usually  harm- 
less. But  they  should  be  avoided  by  children  and  not  used 
to  excess  by  adults. 

Alcohol,  except  possibly  in  exceedingly  small  quantities, 
cannot  be  considered  a  food,  and  as  a  stimulator  for  the 
appetite  it  should  not  be  used.  Many  careful  experiments 
have  shown  that  while  it  may  stimulate  the  body  tempo- 
rarily, it  does  not  enable  it  to  do  more  work.  Instead, 
those  using  it  cannot  do  as  much  work,  or  withstand  as 
great  physical  or  mental  strain,  as  those  not  using  it. 

Even  if  it  were  not  for  the  ungovernable  appetite  which 
its  use  almost  invariably  engenders,  and  for  the  degrading 
influences  with  which  its  use  is  usually  surrounded,  its 
physiological  action  is  such  as  to  lessen  the  body's  vitality. 
decrease  its  resistance  to  disease,  and  dull  its  nervous  and 


432 


FOODS 


mental  efficiency.  So  surely  do  deteriorating  results  follow 
its  steady  use  that  insurance  companies  regard  men  who 
use  alcohol  as  bad  risks.  Railroads  and  many  great  in- 
dustries refuse  to  employ  users  of  alcohol. 


ei® 

%^ 


COFFEE  PLANT 
Showing  the  clusters  of  beans  from  which  coffee  is  produced. 

Whatever  scientists  may  conclude  as  to  the  food  value  of 
minute  quantities  of  alcohol,  they  agree  that  as  a  steady 
"  stimulating  "  beverage,  it  must  be  classed  as  a  poison. 

Careful  scientific  experiments  have  also  been  made  upon 
the  effect  of  tobacco.  Although  there  are  differences  of 


PREPARATION  OF  FOODS  433 

opinion  about  its  effect  upon  fully  matured  adults,  there 
is  no  such  difference  of  opinion  in  regard  to  its  effect  upon 
those  who  have  not  stopped  growing  and  are  not  yet  fully 
matured. 

Measurements  and  comparisons  made  in  regard  to  the 
physical  development,  endurance,  and  mental  ability  of 
a  large  number  of  college  men  have  shown  conclusively  that 
those  who  have  not  used  tobacco,  as  a  rule,  have  better 
physiques,  are  better  students,  and  can  stand  more  physical 
exercise  than  those  who  have  used  it.  In  the  competition 
for  athletic  teams  it  is  found  that  only  about  half  as  many 
of  those  who  have  used  tobacco  make  good,  as  of  those  who 
have  not  used  it. 

Preparation  of  Foods.  —  When  foods  are  appetizing, 
look  good,  smell  good,  and  taste  good,  both  the  saliva  and 
the  gastric  juice  are  secreted  in  larger  quantities,  so  that 
this  sort  of  food,  when  taken  into  the  system,  is  more  read- 
ily digested  than  food  which  is  not  attractive.  One  of  the 
reasons  for  cooking  food  is  to  render  it  appetizing,  and 
this  should  never  be  lost  sight  of  by  the  cook.  Cooking 
also  softens  and  loosens  the  fibers  of  meats  and  causes  the 
cell  walls  of  the  starch  granules  to  burst,  thus  rendering 
it  possible  for  the  digestive  juices  to  attack  the  food  more 
readily.  In  addition,  cooking  kills  the  germs  and  other 
parasites  that  are  sometimes  found  in  foods. 

To  cook  food  properly  is  a  fine  art  and  requires  most 
careful  study  and  great  skill.  The  science  of  providing 
economically  the  kinds  of  food  necessary  and  of  cooking 
these  properly  so  that  they  will  be  attractive,  easily  digested 
and  will  lose  none  of  their  nutritive  value,  is  one  that  is  at 
present  in  its  infancy.  Human  beings,  like  other  animals, 


434 


FOODS 


ANCIENT  COOKING  UTENSILS 

must  have  a  balanced  ration  or  diet  if  they  are  to  be  most 
productive  economically.  They  differ  from  other  animals 
in  having  a  much  greater  range  of  food  possibilities  and  in 
being  much  more  sensitive  as  to  the  appearance  and  taste 
of  food. 


ONE  DAY'S  BALANCED  RATION  FOR  FIVE  PERSONS 


PLANTS  THAT  CHANGE  FOOD 


435 


Plants  That  Change  Food.  —  If  it  were  not  for  microscopic 
plants  (page  398),  food  would  keep  indefinitely  without 
change.  These  little  plants  are,  however,  present  every- 
where and  if  conditions  are  suitable  for  their  growth  they 
begin  at  once  to  change  or  to  "  spoil  "  all  foods  they  can 
reach.  Some  of  the  bacterial  changes  make  food  more 


BREAD  MOLD.     (Greatly  magnified.) 

palatable,  for  it  is  bacteria  that  give  the  fine  flavors  to  the 
best  butter  and  cheeses  and  the  gamy  flavor  to  certain  kinds 
of  meat.  Bacteria  also  change  cider  into  vinegar. 

Experiment  143  (Teacher's  Experiment).  —  Make  a  solution  of 
molasses  and  water.  Place  some  yeast  in  it  and  put  the  mixture 
away  in  a  warm  place.  Watch  it  for  a  few  days,  and  after  gas 
bubbles  have  been  coming  off  for  some  time  put  the  solution  in  a 
flask  connected  with  a  distilling  apparatus,  as  shown  in  Figure  136. 
Gently  heat  the  solution  and  collect  the  distillate.  Smell  of  the 
distillate.  What  does  it  smell 'like?  Dip  a  piece  of  cotton  cloth 
in  it  and  touch  a  lighted  match  to  it.  If  the  experiment  has  been 
successful,  the  distillate  will  burn.  If  not,  distill  some  of  the 
distillate  again.  Alcohol  and  carbon  dioxide  are  produced  by  the 
action  of  the  yeast  on  the  molasses  and  the  alcohol  is  evaporated 
by  low  heat  and  condensed  in  the  still. 


436 


FOODS 


The  ancient  Egyptians  knew  that  if  flour  was  mixed  with 
water  and  left  in  a  warm  place  it  would  soon  become 
porous ;  and  that  if  pieces  of  this  porous  dough  were  put  into 


FIGURE  136 

other  dough,  they  would  make  this  dough  become  porous 
more  quickly.     These  pieces  of  dough  were  called  leaven, 
and  the  leavened  bread  of  the  ancients  was  made   in  this 
way.     Even  to-day  in  some  countries  this  method  is  fol- 
lowed.      The     Romans 
sometimes  used  a  leaven 
made  out  of  grape  juice 
and    millet.      In     these 
methods,  the  wild  yeast 
plants    which    exist    al- 
most everywhere  in  the 
air    found    a    favorable 

lodging  in  the  prepared  substance,  and  by  their  growth 
and  activities  "  raised  "  the  bread.  Later,  methods  were 
devised  for  cultivating  the  yeast  plants,  and  the  making 
of  "  raised  "  bread  became  common. 


YEAST  PLANTS 


PLANTS  THAT  CHANGE  FOOD  437 

In  modern  bread  making,  yeast,  which  contains  the 
minute  yeast  plants,  is  mixed  thoroughly  into  the  material 
which  is  to  compose  the  bread ;  and  the  bread  is  then  put 
into  a  warm  place  to  rise  —  or,  more  exactly,  to  allow  the 
yeast  plants  to  multiply.  If  the  materials  and  the  tem- 
perature are  right,  the  yeast  plants  multiply  very  rapidly, 
feeding  upon  the  material  of  the  dough,  and  changing  sugar 
into  carbon  dioxide  and  alcohol.  Little  bubbles  of  carbon 
dioxide  gas  are  developed  throughout  the  dough,  making 
it  slightly  porous. 

The  dough  is  then  kneaded  to  develop  the  elasticity  of 
the  gluten  and  to  mix  the  greatly  increased  number  of  yeast 


BREAD  MAKING  IN  MEXICO 

plants  uniformly  through  the  mass.  It  is  then  set  aside 
again  so  that  the  uniformly  scattered  yeast  plants  may  con- 
tinue their  activities.  Bubbles  of  carbon  dioxide  form 
throughout  the  whole  mass,  and  a  light  spongy  dough 
results.  When  this  is  heated  in  the  oven,  the  tiny  bubbles 
of  gas  expand,  making  a  more  porous  sponge,  the  alcohol 
evaporates,  and  the  dough  bakes,  thus  forming  light  bread. 


438  FOODS 

Sometimes  other  substances  besides  yeast  are  used  to 
generate  the  carbon  dioxide  necessary  to  raise  the  dough. 
In  Experiment  26,  it  was  found  that  the  action  of  an  acid 
on  certain  substances  liberated  carbon  dioxide.  Often  in 
making  biscuits  and  cake,  soda  and  sour  milk  are  used. 
The  gas  is  liberated  by  the  action  of  the  acid  in  the  sour 
milk  upon  the  baking  soda.  Baking  powder,  which  usually 
consists  of  baking  soda  and  cream  of  tartar  mixed  with  corn- 
starch,  is  also  used.  When  the  baking  powder  is  mixed 
with  flour  and  moistened,  the  cream  of  tartar  acts  like  an 
acid  upon  the  soda,  liberating  carbon  dioxide  and  thus 
causing  the  dough  to  rise.  As  in  bread,  the  gas  is  expanded 
by  the  heat  of  the  oven,  making  the  cake  or  the  biscuits 
more  porous. 

Most  of  the  minute  plants  which  cause  changes  in  food 
render  it  unfit  for  man's  use.  We  have  found  that  decay, 
which  is  caused  by  bacteria,  is  on  the  whole  a  friendly  pro- 
cess. But  we  look  upon  it  as  an  unfriendly  process  when 
it  results  in  the  souring  of  milk,  the  tainting  of  meat,  the 
spoiling  of  eggs,  and  the  rotting  of  vegetables  —  all  of 
which  are  due  to  the  activities  of  bacteria. 

The  decay  in  fruit,  the  mold  on  bread,  the  corn  smut, 
the  smut  on  oats  and  barley,  the  potato  blight,  the  scabs 
of  apples  and  potatoes,  the  rusts  on  grains,  and  many  other 
common  plant  diseases  are  simply  fungous  plant  growths. 
The  wheat  rust  alone  costs  the  United  States  many  millions 
of  dollars  each  year.  Thousands  of  feet  of  timber  are  de- 
stroyed yearly  by  the  wood-destroying  fungi.  Dry  rot  of 
timber,  as  it  is  called,  is  due  to  a  fungous  growth.  The  fight 
against  these  harmful  fungi  costs  millions  of  dollars  each  year. 

Experiment  144.  —  Place  a  slice  of  freshly  boiled  potato  in  each 
of  six  clean,  4-ounce,  wide-mouthed  bottles.  Close  the  mouths  of 


PLANTS  THAT   CHANGE   FOOD  439 

the  bottles  with  loose  wads  of  absorbent  cotton.  Place  five  of 
these  bottles  in  a  sterilizer  and  sterilize  for  half  an  hour.  Allow 
the  sixth  bottle  to  remain  unsterilized.  (A  sterilizer  can  be  made 
by  taking  a  covered  tin  pail  and  putting  into  the  bottom  of  it  a 
bent  piece  of  tin  with  holes  punched  in  it  to  act  as  a  shelf  on  which 
to  put  the  bottles.  A  shallow  tin  dish  with  holes  in  it  is  good  for 
the  shelf.  There  must  be  holes  so  that  the  steam  will  not  get  under 
the  shelf  and  upset  it.  Fill  the  sterilizer  with  water  to  the  top  of 
the  shelf  and  place  the  bottles  on  the  shelf.  Keep  the  water  boil- 
ing.) A  reliable,  inexpensive  sterilizer  is  the  pressure  cooker  shown 
on  page  126. 

Take  the  bottles  out  and  allow  them  to  cool.  Ptemove  the  cotton 
from  one  of  them  for  several  minutes  and  then  replace.  Run  a 
hat  pin  two  or  three  times  through  the  flame  of  a  Bunsen  burner  to 
sterilize  it  and  place  it  in  the  water  of  a  vase  which  has  had  flowers 
in  it  for  some  time.  Carefully  pulling  aside  the  edge  of  the  absorb- 
ent-cotton stopper  hi  the  second  bottle,  insert  the  pin  and  place 
a  drop  of  the  vase  water  on  the  surface  of  the  piece  of  potato. 
After  having  sterilized  the  pin  again,  rub  it  several  times  over  the 
moistened  palm  of  the  hand  and  then,  using  the  same  precautions 
as  before,  scratch  the  potato  in  the  third  bottle.  Put  a  fly  in  the 
fourth  bottle,  using  the  same  precautions.  Keep  the  fifth  bottle 
just  as  it  was  taken  from  the  sterilizer  as  an  indicator,  that  is, 
to  see  whether  the  bottles  were  thoroughly  sterilized.  Put  all 
of  the  bottles  away  in  a  warm  place  and  observe  them  each  day  for 
several  days.  The  spots  appearing  on  the  pieces  of  potato  are 
bacteria  colonies. 

Since  bacteria  and  fungi  cause  the  "  spoiling  "  of  food, 
and  since  certain  bacteria  develop  poisons  called 
ptomaines  which  make  the  eating  of  the  food  infected  very 
dangerous,  it  is  necessary  that  food  be  protected  as  far  as 
possible  from  bacteria  and  that  their  growth  be  checked. 
Food  should  never  be  handled  except  with  clean  hands; 
it  should  be  most  carefully  protected  from  dust  and  flies 
and  kept  in  a  clean,  cool  place.  Most  bacteria  do  not  thrive 
where  it  is  cold. 


440 


FOODS 


Preserving  Food.  —  When  it  is  desired  to  preserve  food 
for  a  long  time,  especial  care  must  be  taken.  It  has  been 
found  that  thoroughly  drying  food  will  protect  it  against 
bacteria ;  that  freezing  or  smoking  fish  and  meat  preserves 
them ;  that  salt  and  vinegar  and  spices  act  as  preservatives ; 
that  if  fruits  and  vegetables  are  heated  for  some  time  at  a 
boiling  temperature  and  tightly  sealed  in  cans  they  will 

keep ;  that  fruits  do 
not  spoil  if  placed  in 
strong  sugar  sirups; 
that  fruits  and  vege- 
tables and  eggs  can  be 
kept  without  spoiling 
where  the  tempera- 
ture is  maintained 
at  a  little  above  the 
freezing  point. 

In  all  these  cases 
the  bacteria  in  the 
food  are  either  en- 
tirely destroyed  and 
the  food  is  absolutely 
protected  from  other 

bacteria,  or  else  the  growth  of  the  bacteria  is  completely 
checked.  Sometimes  eggs  are  preserved  for  a  considerable 
time  by  placing  them  in  a  waterglass  solution.  In  this 
case  the  waterglass  fills  up  the  tiny  pores  in  the  shell  of  the 
egg  and  keeps  out  the  bacteria  just  as  paint  keeps  them 
out  of  wood.  In  the  case  of  the  egg,  however,  there  is  plenty 
of  moisture  within  the  egg  for  the  growth  of  whatever  bac- 
teria may  be  present,  whereas  in  painted  dry  wood  the 
moisture  is  kept  out  and  the  bacteria  are  unable  to  grow. 


PREPARING  SMOKED  FISH  AT  GLOUCESTER 


BACTERIAL  DISEASES 


441 


In  order  to  keep  bacteria  from  spoiling  meat,  borax  is 
sometimes  used.  Formalin  is  sometimes  put  into  milk 
to  keep  it  from  souring,  and  benzoate  of  soda  into  catsups 


Courtesy  of  Beech^Nvt  Packing  Co. 

STERILIZING  CATSUP  AND  CHILI  SAUCE 

The  metal  baskets  filled  with  bottles  of  chili  sauce  and  catsup  are  lowered 
into  the  sterilizing  tanks,  which  are  constructed  on  the  principle  of  the 
pressure  cooker  (page  126).  Notice  the  abundant  lighting  and  scrupu- 
lous cleanliness  of  the  room. 


for  the  same  reason.  These  three  substances  act  as  preserv- 
atives, but  they  also  make  the  food  unwholesome  and  so  we 
have  pure  food  laws  prohibiting  the  use  of  such  preserva- 
tives for  foods. 

Bacterial  Diseases. — Out  of  the  fifteen  hundred  or  more 
kinds  of  bacteria  that  are  known,  only  about  seventy  may 
grow  in  our  bodies  and  make  us  ill.  Most  of  the  others  are 


442  FOODS 

man's  efficient  helpers.  These  disease-causing  bacteria,  how- 
ever, may  cause  a  vast  amount  of  trouble.  The  microscopic 
plants  and  animals  that  cause  disease  are  commonly  called 
germs. 

Almost  all  disease  germs  get  into  the  body  through  a 
break  in  the  skin  or  through  the  mouth  or  nose.  The  skin 
when  unbroken  is  a  splendid  germ  armor.  When  it  is 
broken  the  bacteria  have  a  chance  to  enter.  In  the  ma- 
jority of  cases  there  are  not  enough  hostile  bacteria  at  hand 
to  make  serious  trouble ;  but 
there  is  always  a  chance  of  their 
being  present,  and  so  all  wounds 
ought  to  be  cleansed,  disinfected 
and  dressed  with  absorbent 
cotton,  or  some  similar  sub- 
stance. We  found  in  Experi- 
ment 144  that  absorbent  cotton 
kept  the  bacteria  out.  If  wounds 
are  not  given  careful  attention, 
blood-poisoning,  which  is  a  bac- 

FIRST  AID  KIT  .    ,  j.  .         0 

tenal  disease,  may  set  in.  Some- 
times when  a  rusty  nail  or  other  dirty  substance  breaks 
through  the  skin,  bacteria  are  carried  into  the  flesh.  If 
such  a  wound  is  not  properly  disinfected  and  cared  for, 
lockjaw,  another  bacterial  disease,  may  be  developed. 

By  getting  into  the  body  through  the  mouth  or  nose, 
bacteria  cause  many  other  diseases.  Among  these  are 
influenza  (grippe),  diphtheria,  pneumonia,  whooping-cough, 
typhoid  fever,  and  tuberculosis.  People  having  diseases  of 
these  kinds  throw  off  a  great  number  of  bacteria.  If  such 
germs  get  into  the  bodies  of  other  people,  they  may  cause 
the  same  diseases  there.  Disease  germs  usually  do  not 


BACTERIAL  DISEASES  443 

float  in  the  air  for  any  great  distance  from  the  diseased  person. 
But  danger  lurks  in  handling  articles  infected  by  germs, 
from  eating  infected  food,  or  from  drinking  infected  water. 

All  dishes  and  utensils  used  by  persons  having  contagious 
or  infectious  diseases  should  be  kept  by  themselves,  washed 
in  boiling  water,  and  not  used  by  other  people.  All  their 
bedding  and  clothing  should  be  thoroughly  washed  in  some 
disinfectant,  boiled  if  possible,  and  hung  for  some  time  in 
direct  sunlight.  Rooms  should  be  disinfected  before  they 
are  used  by  other  persons.  In  very  contagious  diseases 
mattresses  and  materials  which  cannot  be  disinfected  should 
be  burned.  As  all  germ  diseases  are  spread  by  sick  people, 
epidemics  can  be  prevented  if  sufficient  care  is  taken. 

So  closely  are  people  brought  together  in  our  towns  and 
cities  that  carelessness  on  the  part  of  one  may  endanger 
many,  and  it  is  particularly  necessary  that  regulations  be 
enforced  which  shall  protect  society  from  the  careless  spread- 
ing of  disease.  In  some  very  virulent  diseases,  such  as 
smallpox  or  diphtheria,  the  patients  ought  to  be  kept  to 
themselves,  quarantined,  their  rooms  and  everything  about 
them  disinfected,  and  every  precaution  taken  to  prevent 
people  susceptible  to  the  diseases  from  being  exposed  to  the 
germs. 

This  cannot  and  ought  not  to  be  done  in  all  cases  of  bac- 
terial disease,  since  adequate  protection  can  be  given  if 
sufficient  care  is  taken  by  the  person  affected.  If  tubercular 
patients  will  carefully  cover  their  mouths  with  cloths  when 
coughing  or  sneezing  and  see  that  the  cloths  are  burned, 
tubercular  germs  will  cease  to  be  a  menace  to  society.  Al- 
though thousands  are  afflicted  each  year  with  tuberculosis, 
largely  through  the  carelessness  of  those  having  it,  the  disease 
is  readily  preventable  and  curable.  If  the  same  precautions 


444  FOODS 

are  taken  in  whooping  cough  or  grippe,  or  ordinary  "  cold," 
the  infection  will  not  be  spread. 

As  we  said  before,  the  fight  put  up  by  the  white  cor- 
puscles is  not  the  only  fight  the  body  makes  against  bac- 
teria and  their  activities.  When  disease  bacteria  get  es- 
tablished in  the  system,  they  secrete  a  poison  called  toxin, 
which  is  absorbed  by  the  blood  and  carried  throughout 
the  body,  thus  poisoning  many  other  parts  beside  those  im- 
mediately attacked  by  the  bacteria.  The  cells  of  the  body 
at  once  begin  to  secrete  a  substance  to  counteract  this 
poison,  an  antitoxin.  If  the  vitality  of  the  patient  is  great 
enough,  sufficient  antitoxin  will  be  secreted  to  neutralize 
the  effect  of  the  toxin  and  the  disease  will  be  overcome. 

Of  late  years  it  has  been  found  that  these  antitoxins 
can  be  artificially  supplied  or  caused  to  develop.  Thus 
the  system  may  be  aided  in  neutralizing  the  effect  of  the 
toxin,  and  in  warding  off  the  disease.  By  injecting  these 
antitoxins  or  stimulating  their  development,  people  are  now 
protected  against  smallpox,  diphtheria,  and  other  diseases. 
So  carefully  are  these  preparations  made  at  present  that 
if  proper  care  is  taken  in  their  injection,  there  is  almost 
never  any  ill  effect  from  their  use. 

How  to  Disinfect.  —  Most  bacteria  thrive  best  at  a  mod- 
erate temperature  (70°  to  95°  F.).  Almost  all  of  them  are 
killed  if  kept  at  a  boiling  temperature  for  a  short  time. 
They  cannot  grow  where  there  is  no  moisture,  and  all  but 
a  few  kinds  are  killed  by  complete  drying.  Direct  sunlight 
is  soon  fatal  to  them. 

For  disinfecting  wounds,  iodine  or  a  dilute  solution  of 
carbolic  acid  or  lysol  serves  well.  (These  must  not  be  taken 
internally.)  Hydrogen  peroxide  is  a  good  external  cleanser 


DANGERS  FROM  INFECTED  FOOD  AND  WATER      445 

and  has  some  disinfecting  qualities.  Cinders  may  often  be 
washed  out  of  the  eye  and  the  eye  disinfected  with  a  dilute 
solution  of  boracic  acid.  Strong  disinfectants  should  never 
be  used  in  the  eyes  or  nose.  A  solution  of  listerine  is  a 
safe  mouth  wash. 

For  disinfecting  sinks  or  washbowls  a  generous  quantity 
of  boiling  water  containing  a  small  amount  of  carbolic  acid 
or  lysol  is  very  effective.  Chloride  of  lime  is  the  most  com- 
mon disinfectant  for  sewage  pipes  leading  from  bathrooms. 
Woodwork  and  wall  fixtures  may  be  wiped 
with  a  dilute  solution  of  carbolic  acid  or 
formalin.  It  must  be  remembered  that 
some  of  these  household  disinfectants  are 
deadly  poisons  if  taken  internally. 

Rooms  are  disinfected  by  burning  sul- 
phur in  them.  The  sulphur  gas  will  not  be 
effective,  however,  unless  the  atmosphere 
of  the  room  is  very  moist.  Moisture 
can  be  supplied  to  the  atmosphere  by 
thoroughly  spraying  the  room  with  a  fine  FIQU  iyf 
atomizer  or  by  boiling  water  in  it  for  some 
time.  Formaldehyde  candles  (Figure  137)  are  also  burned 
in  rooms  to  disinfect  them.  These  have  proved  quite 
satisfactory.  Soap  and  water,  sunlight  and  air,  are  the 
only  disinfectants  needed  for  rooms  except  in  case  of  con- 
tagious or  infectious  diseases. 

Dangers  from  Infected  Food  and  Water.  —  If  foods  are 
handled  by  diseased  persons  or  by  those  whose  dirty  hands 
have  acquired  disease  bacteria,  or  if  the  foods  are  allowed  to 
stand  exposed  to  dust  and  dirt,  they  collect  germs.  If  the 
food  is  afterward  thoroughly  cooked,  the  germs  are  gener- 


446 


FOODS 


ally  killed.  If,  however,  as  in  the  case  of  bread,  fruit, 
and  some  vegetables,  no  cooking  is  done  before  the  foods 
are  eaten,  the  foods  may  often  carry  disease. 

Milk  is  particularly  liable  to  be  infected  with  disease 
germs  because  they  readily  grow  in  it  and  increase  rapidly. 

Many  epidemics  of 
typhoid  fever,  scarlet 
fever,  diphtheria,  and 
other  germ  diseases 
have  been  directly 
traced  to  polluted 
milk.  Either  the 
milk  came  directly 
from  dairies  where 
these  diseases  existed, 
or  had  been  put  into 
bottles  taken  from  in- 
fected homes  and  not 
afterward  sterilized. 
The  older  such  milk 
becomes  the  greater 
is  the  danger  of  using 
it  since  bacteria  mul- 
tiply in  it  with  such 
tremendous  rapidity. 

Infants  are  particularly  liable  to  contract  diseases  from 
impure  milk  because  this  is  their  main  diet.  Statistics 
show  that  a  large  percentage  of  infant  deaths  are  caused  by 
infected  milk.  If  milk  is  scalded  the  germs  are  killed,  but 
scalding  makes  milk  less  palatable  and  less  digestible. 
When  milk  is  thoroughly  heated  to  a  temperature  of  160° 
F.  for  fifteen  or  twenty  minutes,  the  disease  germs  are 


DANGERS  PROM   INFECTED   FOOD  AND   WATER       447 

killed  but  the  milk  itself  is  not  made  less  digestible  nor  is 
its  taste  affected.  This  is  called  pasteurization.  The 
milk  should  be  cooled  quickly  after  it  is  heated,  covered  with 
absorbent  cotton,  and  kept  in  a  refrigerator  so  that  fresh 
germs  cannot  infect  it.  Pasteurized  milk  „ 

is  the  only  safe  milk  to  use  unless  it  is 
absolutely  known  that  great  care  has  been 
taken  to  keep  the  milk  at  all  times  clean 
and  cold  enough   to  be  safe  from  infec- 
tion.    Certain  cities  require  that  all  milk 
sold  shall  either  come  from  healthy  cows  in 
dairies  of  "  certified "  cleanliness  or  else 
shall    be  pasteurized.     Refrigerators   and    A  SIMPLE  PASTEUR- 
places  where  milk  and  food  are  kept  must        IZINO  °UTFIT 
be  washed  and  thoroughly  scalded  with  hot  water  frequently 
if  they  are  to  be  kept  free  from  bacterial  infection. 

Water  is  also  a  dangerous  carrier  of  bacteria.  Water 
from  deep  artesian  wells  is  usually  safe,  but  streams  that 
flow  over  the  surface  of  the  ground  continually  have  washed 
into  them  materials  which  contain  germs.  Unless  great 
care  is  taken  to  keep  surface  water  out  of  springs  or 
wells  and  to  keep  the  drainage  from  stables  and  out- 
buildings from  seeping  into  them,  they  become  dangerous 
as  sources  of  water  supply.  Impure  water  is  an  ever  active 
source  of  disease  and  one  that  cannot  be  too  carefully 
watched. 

Many  of  our  large  cities  have  in  recent  years  expended 
vast  sums  of  money  upon  their  water  supplies  in  order  that 
citizens  may  be  protected  as  far  as  possible  from  disease. 
The  drainage  canal  which  Chicago  built  at  great  expense  to 
divert  its  sewage  from  Lake  Michigan  greatly  lowered  the 
death  rate  from  typhoid  fever  in  that  city.  Further  de- 


448 


FOODS 


crease  in  typhoid  and  intestinal  diseases  in  Chicago  is  due  to 
the  fact  that  a  large  part  of  the  milk  which  is  now  used  there 
is  pasteurized.  Care  concerning  these  two  most  important 
supplies,  water  and  milk,  has  greatly  decreased  the  death 
rate  in  many  American  cities  during  the  present  century. 
It  is  estimated  that  the  actual  money  loss  each  year  in  the 


A  WELL  WITH  CONTAMINATED  WATER  SUPPLY 

United  States  because  of  the  ravages  of  preventable  diseases 
is  between  one  and  two  billion  dollars. 

When  there  is  any  doubt  about  the  purity  of  water  it 
should  be  boiled.  This  will  kill  the  dangerous  bacteria. 
Ordinary  house  filters  are  useless  and  often  worse  than  use- 
less, as  they  simply  become  breeding  places  for  bacteria. 
They  may  make  the  water  look  clearer  but  they  do  not 
destroy  the  bacteria ;  and  it  is  the  bacteria,  not  the  solid 
matter,  that  constitute  the  real  danger. 


SEWAGE   DISPOSAL 


449 


Bacteria  can  live  and  grow  in  such  minute  cracks  that 
to  use  dishes  washed  in  impure  water  is  about  as  dangerous 

as  to  drink  the  water.     All  public  towels      

and  drinking  cups  should  be  abolished. 
Experiments  have  shown  that  even  drinking 
fountains  unless  most  carefully  constructed 
are  liable  to  retain  in  the  pipes  germs  left 
by  other  users.  The  use  of  the  individual 
cup  is  the  one  safe  method  for  drinking. 


Sewage  Disposal.  —  The  proper  disposal          ""( 
of  human  waste  is  a  vital  problem.     Ex- 
posure to  wind  and  flies  allows  the  germs  in  it  to  be  spread 
about.     The  waste  must  therefore  be  disposed  of  in  some 
wav  or  disinfected.     On  the  farm  or  in  small  towns  where 


Courtesy  of  Department  of  PtMie  Wort*.  Colttmtnu.  OHIO 

SEWAGE  DISPOSAL  BED,  SOLIDS 


450  FOODS 

running  water  can  be  supplied,  cesspools  and  septic  tanks 
answer  the  purpose.  In  cities,  however,  most  complicated 
systems  of  sewage  disposal  must  be  employed.  In  the 
most  healthful  cities  the  sewage  is  gathered  from  all  -parts 
of  the  city  by  means  of  water  flowing  in  underground  sewers. 
In  seaboard  cities  the  sewers  usually  empty  into  the  sea  and 
the  tides  and  currents  dispose  of  the  sewage. 


Courtesy  of  Department  of  Public  Works,  Columbus,  Ohio 
SEWAGE  DISPOSAL,  LIQUIDS 

Cities  upon  large  rivers  frequently  empty  their  sewage 
into  the  rivers,  but  this  pollutes  the  water  far  downstream. 
A  very  much  better  way  than  this  has  of  late  years  been 
devised  and  is  being  used  by  many  inland  cities.  Sewage 
disposal  plants  are  built,  where  the  sewage  is  run  into  large 
tanks  and  the  solid  matter  is  decomposed  by  the  action 
of  certain  kinds  of  bacteria.  The  liquid  is  then  slowly 


CLEANLINESS 


451 


filtered  through  beds  of  sand  and  gravel,  and  the  sewage  is 
thus  freed  of  organic  impurities. 

Cleanliness.  —  Every  year  we  are  learning  more  and  more 
about  disease.  The  World  War  has  demonstrated  in  a 
wonderful  manner  the  advances  which  have  been  made  in 


A  PRIMITIVE  WASHING  SCENE  IN  MEXICO 

life  saving  as  well  as  in  life  destruction.  Diseases  like  small- 
pox, typhoid  fever,  and  bubonic  plague,  which  were  for- 
merly dreaded  so  greatly  by  armies,  have  been  practically 
eradicated.  Wounds  which  only  a  few  years  ago  were  al- 
ways fatal  are  now  easily  healed.  All  of  this  has  come  about 
because  of  our  increased  knowledge  of  disease  germs  and 
how  to  combat  them. 


452 


FOODS 


Prominent,  however,  above  everything  else  stands  out 
the  fact  that  cleanliness  is  the  great  protector  of  health. 
Those  communities  that  have  well-built  sewers,  clean  streets, 
clean  milk,  and  clean  water  are  healthy.  The  community 
through  its  boards  of  health  must  protect  the  individual 
from  the  germs  of  contagious  and  infectious  diseases,  for 
he  cannot  do  this  by  himself.  Persons  that  eat  pure  food, 
drink  pure  water,  breathe  pure  air,  and  keep  their  bodies 
pure  are  usually  healthy. 

The  Americans  were  able  to  build  the  Panama  Canal 
because  they  were  able  to  protect  the  workmen  from  disease 
germs.  Disease  had  defeated  previous  attempts.  They 
were  able  to  make  Havana,  Cuba,  a  healthy  and  healthful 
city  —  although  for  years  it  had  been  one  of  the  plague 

spots  of  the  world 
—  by  cleaning  it  up 
and  destroying  the 
breeding  places  of 
disease  germs. 

Animal  Life  that 
Causes  or  Spreads 
Disease.  —  Certain 
low  forms  of  animal 
life,  the  protozoa, 
have  already  been 
mentioned  as  disease  producers.  Unlike  bacteria,  the  pro- 
tozoa do  not  cause  disease  by  passing  directly  from  one 
person  to  another.  Instead,  they  need  to  live  in  some  insect 
between  whiles.  In  malaria  and  yellow  fever  the  insect 
in  which  they  live  is  the  mosquito,  and  in  the  sleeping  sick- 
ness they  live  in  a  fly  called  the  tsetse.  If  a  mosquito  of 


A  DISEASE-BEARING  MOSQUITO 
The  mosquito  is  greatly  magnified. 


ANIMAL  LIFE   THAT   SPREADS  DISEASE         453 


the  right  species  bites  a  person  afflicted  with  malaria  or 

yellow  fever,  some  of  these  little  animals,  the  protozoa,  are 

sucked   up  with    the   blood   and   enter 

the  mosquito.     They  grow  in  its  body, 

undergoing  several  changes,   until  the 

animal  germs  are  ready  to  be  injected 

into  their  victim,  when  they  pass  into 

the  salivary   glands  of    the    mosquito. 

In  biting,  the  mosquito  always  injects 

a  little  saliva  into  the  wound  and  with 

this   go    the   germs.     These  enter  the 

blood,  multiply  rapidly,  and  cause  the 

disease. 

If  mosquitoes  can  be  kept  from  biting 
people  who   have  these  diseases  or  if 
infected  mosquitoes  can  be  kept  from  biting  other  people, 
such    diseases  will    not   spread.     The   best   way   to   keep 


AMCEBA  DIVIDING 


A  "MALARIAL"  SWAMP 
A  breeding  place  for  moaquitoea. 


454 


FOODS 


mosquitoes  from  biting  is  to  exterminate  them.  Since 
mosquitoes  breed  in  stagnant  water,  all  old  ditches  or 
small  pools  where  water  accumulates  should  be  emptied  and 
drained.  Larger  stagnant  pools  should  be  drained  or  have 
a  film  of  kerosene  spread  over  their  surface  by  frequently 
pouring  a  little  of  the  oil  on  the  water.  This  will  keep  the 
mosquitoes  from  breeding  and  prevent  the  diseases. 

The  Texas  fever,  which  has  caused  such  great  financial 
losses  to  the  cattlemen  of  the  United  States,  is  caused  by  a 
protozoan  injected  into  the  cattle  by  the  bite  of  a  tick. 

Bubonic  plague,  the  "  Black  Death  "  that  swept  Europe 
during  the  Middle  Ages,  is  spread  by  the  bite  of  a  flea  that 
lives  on  plague-infested  rats.  Hundreds  of  thousands  of 
dollars  have  been  spent  by  the  Government  in  killing  rats 
in  some  of  the  ports  of  the  United  States  where  the  plague 
has  succeeded  in  landing.  Many  seaports  are  now  rat- 
proofing  their  wharves  in  an  effort  to  exterminate  these  pests. 
The  cables  holding  ships  to  the 
docks  are  often  passed  through 
holes  in  the  centers  of  metal 
sheets  in  order  to  prevent  rats 
from  entering  a  ship  by  walking 
along  the  cables.  Sailors  have 
learned  that  if  the  rats  are  kept 
out,  the  plague  is  kept  out. 

Flies.  —  The   words  fly  and 

HOUSE  FLY  (Magnified)  filth   are    almost    synonymous. 

Flies  breed  in  any  kind  of  de- 
caying vegetable  or  animal  matter.  The  eggs  hatch  in 
about  a,  day  and  the  little  white  maggots  after  absorbing 
filth  for  about  ten  days  change  into  adult  flies  with  their 


HEALTH   HINTS 


455 


hairy  bodies  and  sticky  feet,  especially  adapted  for  carrying 
all  kinds  of  germs  and  for  spreading  them  over  everything 
they  touch.  The  fly  delights  to  feed  on  all  kinds  of  foul  or 
diseased  objects,  and  the  waste  it  deposits  is  often  full  of 
dangerous  germs. 

"  Swat  the  fly  "  is  indeed  a  proper  slogan.  But  a  still 
better  plan  would  be  to  destroy  all  filth  or  to  dispose  of  it 
so  as  to  prevent  flies  from  breeding.  Flies  never  travel  far 
and  their  presence  indicates  filth  in  the  neighborhood.  If 
manure  and  other  decaying  matter 
is  kept  in  covered  pits  until  it  is 
used  for  fertilizing,  and  if  garbage 
cans  are  kept  covered,  much 
more  will  be  done  to  exterminate 
the  fly  than  by  swatting.  Houses 
should  be  carefully  screened  and 
all  food  kept  covered  from  these 
carriers  of  disease,  but  along  with 
all  precautions  to  avoid  the  fly 
must  go  consistent  efforts  to 
exterminate  the  fly. 


BACTERIA  COLONIES 
These  were  developed  from  the 
tracks  of  a  fly  on  a  gelatine 
plate. 


Health  Hints.  —  Good  health  is  man's  greatest  asset. 
If  he  is  to  attain  his  highest  power  he  must  maintain  his 
health.  His  muscles  must  be  exercised  so  as  to  stimulate 
the  cells  to  grow  and  to  throw  off  their  waste  products. 
The  skin  must  be  frequently  bathed  so  as  to  remove  the  dirt 
and  waste  materials  that  clog  the  pores.  The  body  must 
have  sufficient  rest  and  sleep  so  that  the  cells  will  not  be 
worn  out  faster  than  they  can  be  reproduced. 

One  must  have  plenty  of  food  but  not  too  much,  or  the 
stomach  and  other  organs  will  suffer  from  overwork.  The 


456  FOODS 

use  of  stimulants,  such  as  tobacco,  alcohol,  and  all  other 
harmful  drugs  must  be  avoided  since  all  of  these  interfere 
with  the  proper  growth,  development,  and  work  of  the 
various  cells  of  the  body.  The  cure-all  patent  medicines, 
which  do  not  cure  at  all  but  which  simply  dope  the  sen- 
sibilities of  the  individual,  should  be  shunned  as  poison. 
Fresh  air  and  sunshine  are  the  best  and  surest  preventives 
of  disease;  and  when  these  are  combined  with  proper  rest, 
food,  clothing,  exercise,  and  bodily  cleanliness,  there  is  little 
danger  of  sickness  except  from  highly  contagious  diseases. 

Every  day  each  person  probably  receives  into  his  system 
thousands  of  disease  germs.  Usually  it  is  only  when  the 
vitality  of  the  body  is  low  that  these  germs  are  able  to  es- 
tablish themselves.  Right  living  is  the  great  disease  pre- 
venter. 

SUMMARY 

The  elements  which  enter  into  the  composition  of  the 
human  body,  such  as  hydrogen,  oxygen,  nitrogen,  carbon, 
etc.,  are  comparatively  few  and  are  abundant  in  the  world 
about  us.  As  foods  they  are  found  in  three  classes  of 
compounds,  carbohydrates,  fats,  and  proteins.  All  foods 
furnish  energy  when  they  are  oxidized  in  the  human  body. 
Proteins  are  especially  needed  for  growth  and  repair  of 
tissues ;  but  since  it  is  easier  for  the  body  to  throw  off  wastes 
from  oxidized  carbohydrates  and  fats,  these  should  constitute 
the  largest  part  of  our  energy-producing  diet.  Men  exposed 
to  cold  need  sugar  and  fats  in  greater  abundance  than 
those  who  live  much  indoors  or  in  warm  climates.  Foods 
containing  iron,  phosphorus,  lime,  and  vitamins  are  also 
essential  in  the  diet  of  all  persons.  Spices,  tea,  and  coffee 
should  be  used  in  moderation  by  adults  and  avoided  by 


SUMMARY  457 

children.  Tobacco  is  positively  harmful  to  immature 
persons,  and  alcohol  as  a  beverage  or  common  stimulant 
must  be  classed  as  a  poison.  Proper  cooking  renders  most 
food  both  more  palatable  and  more  digestible. 

Microscopic  dependent  plants  cause  changes  in  food.  The 
yeast  plant  is  employed  in  bread  making;  certain  bacteria 
change  cider  to  vinegar ;  and  others  are  responsible  for  the 
fine  flavors  of  the  best  butter,  cheeses,  and  certain  kinds 
of  meat.  Still  other  bacteria  cause  foods  to  spoil.  To 
preserve  food  against  such  bacteria,  we  dry  it,  freeze  it, 
smoke  it,  boil  it,  and  seal  it  in  air-tight  receptacles ;  or  employ 
sugar,  salt,  spices,  or  vinegar  as  preservatives. 

Some  bacteria  enter  the  body  and  cause  diseases.  This 
explains  why  we  disinfect  wounds,  quarantine  persons  suf- 
fering from  infectious  diseases,  and  cleanse  thoroughly  or 
destroy  all  household  articles  with  which  such  people  come 
in  contact.  The  body  fights  disease  germs  by  means  of  the 
white  corpuscles  of  the  blood  and  by  means  of  antitoxin 
secreted  by  the  cells  of  the  body.  Every  household  should  be 
supplied  with  certain  common  disinfectants;  and  every 
household  and  community  should  guard  against  infected 
food  and  water,  and  attend  to  the  proper  disposal  of  waste 
and  sewage.  One  of  the  most  effective  means  of  combating 
or  preventing  disease  is  to  maintain  cleanliness. 

Flies  are  great  carriers  of  disease  bacteria,  and  certain 
kinds  of  mosquitoes,  fleas,  and  other  insects  cause  diseases 
by  injecting  disease-producing  protozoa  into  the  blood  of 
victims. 

Exercise,  bathing,  nutritious  food,  proper  clothing,  fresh 
air,  sunshine,  sufficient  rest  and  sleep,  avoidance  of  harmful 
stimulants  and  drugs,  shunning  of  cure-all  patent  medicines, 
and  cheerfulness  are  among  the  essentials  to  health. 


458  FOODS 

QUESTIONS 

What  are  the  three  great  groups  into  which  foods  are  divided  ? 

Why  are  fruits  and  vegetables  so  necessary  ? 

Why  should  not  alcohol  and  tobacco  be  used  ? 

What  are  the  advantages  derived  from  proper  cooking? 

What  is  the  value  of  yeast  in  bread  making?  Describe  and 
give  reasons  for  the  process  usually  employed  in  bread  making. 

Why  are  some  bacteria  and  other  minute  plants  so  harmful? 

How  can  food  be  preserved  and  kept  wholesome  ? 

What  should  one  do  to  protect  himself  from  bacterial  diseases? 

How  should  milk  and  water  be  cared  for?     Why? 

Why  is  cleanliness  so  essential  to  health? 

Why  should  people  take  especial  care  to  protect  themselves  from 
mosquitoes  and  flies? 


CHAPTER  XV 

MAN'S  INVENTIONS  FOE  TRANSFERRING   AND  TRANS- 
FORMING ENERGY 

Tools.  —  Primitive  man  early  found  that  it  was  to  his 
advantage  to  use  something  besides  his  own  hands  and  feet 
to  apply  his  energy.  Probably  the  first  tool  that  he  used 
was  a  stone  which  he  threw  at  some  animal  he  wished  to 
kill  for  food.  Soon  he  found  m 

that  if  he  put  the  stone  in 
a  strip  of  hide  and  swung 
it  around  his  head,  he  could 
send  it  with  greater  force. 
Thus  he  invented  the  sling, 
probably  the  first  device 
for  transferring  energy  and 
the  first  war  machine. 

Since  then  he  has  not 
only  invented  many  ma- 
chines that  have  enabled 
him  to  exert  his  own  physi- 
cal energy  to  greater  advantage,  but  he  has  also  devised 
machines  which  make  it  possible  for  him  to  use  the  energy 
that  exists  in  the  world  about  him.  This  ability  to  utilize 
the  energy  of  nature  has  made  the  life  of  modern  man  very 
different  from  that  of  his  savage  ancestors.  Without  ma- 
chines there  could  be  no  large  cities,  no  manufacturing, 
459 


MAN'S  FIRST  WAR  MACHINE 


460     TRANSFERRING  AND  TRANSFORMING  ENERGY 


HAND  GRENADE  THROWING 
The  utilization  of  hand  throwing  in  modern  warfare. 

no  transportation  facilities,  none  of  the  conveniences  that 

make  modern  life  comfortable. 

More  and  more  man  is  relying  upon  machines  driven  by 

nature's  energy  to 
do  the  work  he  has 
heretofore  done  by 
his  own  physical 
exertion.  The  mow- 
ing-machine, the  sew- 
ing-machine, and  the 
automobile  are  recent 
examples  of  such  in- 
ventions. All  these 
intricate  devices, 

C/.O.  ISJ/ltUU 

BATTLE  "TANK"  however,  have  a  few 

A  modern  complex  war  machine.  simple     machines    as 


FRICTION 


461 


SPINNING  WHEEL 

A  most  useful  application  of  simple  machines.    Spinning  is  now  done 
by  much  more  complex  machinery. 

their  basis.  These  basic  machines  are  the  lever,  the  wheel 
and  axle,  the  pulley,  the  inclined  plane,  the  wedge,  and 
the  screw. 

Friction.  —  If  we  attempt  to  slide  a  box  along  a  level 
floor,  we  find  that  we  have  to  overcome  resistance  or  do 


462       TRANSFERRING  AND  TRANSFORMING  ENERGY 


work.  If  we  put  rollers  under  the  box  there  is  less  resist- 
ance, but  some  resistance  always  develops  when  two  sur- 
faces are  moved  over  each  other.  This  resistance  is 
called  friction.  The  rougher  the  two  surfaces,  the  more 

the  friction ;  and  the 
smoother  they  are, 
the  less  the  friction. 

To  lessen  friction 
we  make  surfaces 
that  slide  over  each 
other  very  smoothly 
and  oil  them.  Roll- 
ing surfaces  are  found 
to  have  less  friction 
than  flat  surfaces, 
and  so  we  use  ball 
or  cylinder  bearings 
in  bicycles,  automo- 
biles, and  many  other 
machines.  But  no 
matter  what  we  do, 
some  of  the  work 
INDIAN  WEAVING  exerted  on  a  machine 


A  form  of  skilled  manual  labor  which  modern 
machinery  has  almost  done  away  with. 


is  always  used  up  in 
overcoming  friction. 
In  an  efficient  machine  the  friction  is  reduced  in  every 
possible  way  in  order  to  avoid  as  far  as  possible  "  loss  of 
energy."  In  some  of  the  simple  machines,  especially  the 
wedge  and  the  screw,  friction  is  always  so  great  that  the 
machines  are  not  very  efficient. 

The  Lever.  —  Experiment  145.  —  (a)  Bore  a  small  hole  through 
a  meter-stick  at  each  of  the  decimeter  divisions.     Place  on  the  table 


THE   LEVER 


463 


a  small  board  so  that  its  edge  shall  be  even  with  the  edge  of  the 
table.  Weight  or  clamp  the  board  to  the  table.  Into  the  edge  of 
the  board  drive  a  round-finish,  small-headed  nail  so  that  it  will 


FIGURE  138 

project  horizontally  over  the  edge  of  the  table.      Slip  the  nail 
through  the  center  hole  of  the  meter  stick.     (Figure  138.) 

Hang  a  weight  of  400  g.  from  the  first  decimeter  hole.  Find 
out  how  much  weight  will  be  required  at  each  of  several  holes  on 
the  other  side  of  the  nail  in  order  to 
balance  the  400  g.  weight.  In  each  case, 
multiply  the  weight  on  each  side  of  the 
nail  by  its  distance  from  the  nail  and 
compare  the  results.  Lift  one  end  of  the 
meter-stick  10  cm.  above  the  edge  of  the 
table,  and  note  how  far  each  weight 
moves.  Multiply  each  weight  by  the 
distance  it  moved  up  or  down,  and  com- 
pare the  results. 

(6)  Attach  a  small  spring  balance  by  a 
short  string  to  one  of  the  end  holes  of  the 
meter-stick.  Slip  the  nail  through  the 
hole  next  to  it.  Hang  a  weight  of  400  g. 
from  any  one  of  the  other  holes.  Pull 
down  on  the  spring  balance  until  the 
meter-stick  is  in  a  horizontal  position. 
Note  the  pull  on  the  spring  balance  and 
make  the  same  computations  as  in  (a).  Repeat  the  experiment  and 
computations  by  hanging  the  weight  from  several  different  holes. 

(Exact  accuracy  in  these  experiments  would  require  a  considera- 
tion of  the  weight  of  the  meter-stick  itself,  but  for  the  purposes  of 
this  experiment,  results  will  be  nearly  enough  accurate  without  this.) 


FAMILIAR  APPLICATIONS 
OF  THE  LEVER 


464     TRANSFERRING  AND   TRANSFORMING  ENERGY 


The  lever  was  probably  one  of  the  first  machines  used 
by  primitive  man.  He  pried  up  rocks  and  pried  open 
logs  to  get  the  roots  and  small  animals  he  needed.  It 
was  to  him  simply  a  convenient  way  of  using  a  stick.  But 

when  Archimedes, 
the  greatest  mathe- 
matician of  ancient 
times,  worked  out 
the  principle  of  this 
simple  machine,  he 
was  so  much  im- 
pressed with  the 
mechanical  advan- 
tage to  be  derived 
from  its  use  that  he 
said,  "  Give  me  a 
fulcrum  on  which  to 
rest  and  I  will  move 
the  earth." 

He  found,  as  was 
indicated  in  Experi- 
ment 145,  that  the 
longer  the  power  arm 
is  than  the  weight 
arm,  the  greater  is 
the  weight  a  given 
force  can  lift,  but 
the  smaller  the  dis- 
tance it  can  lift  it.  If  the  experiment  could  have  been  accu- 
rately, conducted,  it  would  also  have  proved  that  the  power 
multiplied  by  the  distance  the  power  moves  is  equal  to  the 
weight  multiplied  by  the  distance  the  weight  moves. 


GRINDING  CORN,  SCOTCH  HIGHLANDS 
A  simple  application  of  the  lever. 


WHEEL  AND  AXLE 


465 


Careful  experiment 

has  shown  that  this 

last  statement  is  true 

for  all  machines,  and 

so    it    is    sometimes 

called  the  law  of  ma- 

chines.     It    can    be 

stated     in     another 

way:  What  is  gained 

in  power  is   lost  in 

speed    and    what    is 

gained    in    speed    is 

lost  in  power.    Notice 

the  machines  you  are 

familiar  with  and  ob- 

serve how  this   law 

holds   good.     All   of 

us  are  using  different 

kinds  of  levers  every 

day.     Balances,    scissors,    nutcrackers,   wheelbarrows,   for- 

ceps,   and    the   treadle    of   a    sewing-machine   are   all   ex- 

amples of  levers.      . 

Wheel  and  Axle.  —  The  windlass  used 
to  lift  water  out  of  a  well  and  the  cap- 
stan of  a  boat  are  the  most  familiar 
examples  of.  this  form  of 
machine.  (Figure  139.)  The 
wheel  and  axle  is  simply  a 
modification  of  the  lever. 
(Figure  140.)  The  power 
travels  through  the  distance 
of  the  circumference  of  one  FIGURE  HO 


THE  LEVER  AS  USED  BY  THE  ROMANS  FOR 

WEIGHING 

These  scales  were  dug  up  at  Pompeii  and  are 
about  2000  years  old. 


FIGURE  139 


466     TRANSFERRING  AND   TRANSFORMING  ENERGY 


wheel  (A)  while  the  weight  travels  through  the  distance 
of  the  circumference  of  the  other  wheel,  or  axle  (C).  If 
the  circumference  of  the  power  wheel  is  three  times  the 
circumference  of  the  weight  wheel,  a  force  of  5  pounds 

exerted  on  the  power  wheel 
will  lift  a  weight  of  15 
pounds  on  the  weight  wheel. 

The  Pulley.  —  Experiment 
146.  —  (a)  After  well  oiling 
some  small  pulleys  arrange  one 
of  them  as  in  Figure  141,  hav- 
ing a  weight  of  about  500  g. 
on  one  end  of  the  cord  and  a 
spring  balance  on  the  other. 
Slowly  pull  down  on  the  spring 

FIGURE  141     FIGURE  142     FIGURE  143  balance  and  note   the  readin§ 

on  the  scale .    Allow  the  balance 

to  rise  and  note  the  reading.  Friction  accounts  for  the  difference 
between  the  first  and  the  second  reading  of  the  scale.  Average 
the  two  readings  and  see  how  nearly  the  average  equals  the  weight 
on  the  other  end  of  the  cord.  May  we  say  that  the  force  exerted 
by  the  hand  is  equal  to  the  weight?  Does  the  hand 
move  through  the  same  distance  as  the  weight? 

(6)  Arrange  the  pulleys  as  in  Figure  142.  Allow  the 
balance  to  descend,  noting  the  force  recorded  on  the 
scale.  Pull  up  on  the  balance,  noting  again  the  reading 
on  the  scale.  Find  the  average  between  the  two  forces, 
which  may  be  called  the  true  force.  Is  the  force  now 
exerted  by  the  hand  equal  to  the  weight  ?  If  not,  FIQURE  144 
what  are  the  relations  of  these  two  forces? 

Note  the  distance  moved  by  the  hand  and  also  the  distance 
moved  by  the  weight.  How  do  they  compare  ? 

(c)  Arrange  the  pulleys  as  in  Figure  143.  Make  determinations 
similar  to  those  in  (a)  and  (6).  How  does  the  force  exerted  by  the 
hand  now  compare  with  the  weight  ?  How  does  the  distance  moved 
by  the  hand  compare  with  that  moved  by  the  weight  ? 


THE   PULLEY 


467 


It  is  sometimes  exceedingly  convenient  to  change  the 
direction  of  a  force  even  if  no  other  advantage  is  gained. 
To  do  this,  a  rope  may  be  passed  over  a  wheel,  and  thus 
one  may  by  pulling  down  lift  up  the  weight.  Such  an  ar- 
rangement is  called  a  fixed  pulley.  (Figure  141.)  The  cord 


COMBINATION  OF  PULLEYS  USED  TO  LIFT  HEAVY  BURDEN 

Because  of  the  mechanical  advantage  of  the  pulleys,  relatively  small  power 
is  needed  to  lift  this  electromagnet,  with  tons  of  scrap  iron  clinging  to  it. 

in  passing  around  the  wheel  simply  has  its  direction  changed, 
but  there  is  no  gain  for  the  user  of  the  machine  either  in 
power  or  in  distance. 

If  now  the  pulley  is  arranged  as  in  Figure  142,  it  is  no 
longer  a  fixed  pulley  but  is  movable.  It  is  evident  in  this 
case  that  the  weight  is  supported  not  by  a  single  cord  as  in 
the  fixed  pulley  but  by  two  cords,  the  part  of  the  cord  at- 


468       TRANSFERRING  AND   TRANSFORMING  ENERGY 


tached  to  the  beam 
and  the  part  of  the 
cord  held  by  the 
hand.  The  hand  will 
need  to  move  twice 
as  far  as  the  weight 
is  lifted. 

A  number  of  pul- 
leys may  be  arranged 
as  in  Figure  143  so 
that  the  movable  pul- 
ley with  the  weight 
attached  is  supported 
by  several  cords.  In 
this  case  each  sec- 
tion of  the  cord  sup- 
porting the  movable 
pulley  sustains  its 
proportion  of  the 
weight,  and  the  power 
is  as  many  times  less 
than  the  weight  as 
there  are  cords  sup- 
porting the  movable 
pulley.  But  the  gain 
in  power  means  a  loss  in  distance.  The  power  will  have  to 
travel  as  many  times  farther  than  the  weight  as  there  are 
cords  supporting  the  movable  pulley.  An  arrangement  like 
this  enables  a  small  power  slowly  to  lift  a  large  weight. 

The  Inclined  Plane.  —  When  the  ancient  Egyptians  built 
the  great  pyramids,  it  was  necessary  for  them  to  raise  huge 


INCLINED  RAILWAY,  SWITZERLAND 
A  gigantic  inclined  plane. 


THE   SCREW 


469 


USE  OF  THE  WEDGE 


blocks  of  stone  to  great  heights.  It  would  have  been  next 
to  impossible  for  them  to  do  this  simply  by  using  brute 
force.  Some  simple  machine 
was  necessary.  They  prob- 
ably used  the  same  kind  of 
machine  that  is  used  to-day 
in  rolling  a  barrel  into  a 
wagon  or  in  grading  wagon 
roads  or  railroads  over 
mountain  passes  —  an  in- 
clined plane.  The  more 
gradual  the  inclination  up 
which  the  weight  travels,  the  smaller  the  power  required  to 
lift  the  weight.  Again,  what  is  gained  in 
power  is  sacrificed  in  distance. 

The  Wedge. —The  wedge  consists 
simply  of  two  inclined  planes  placed  back 
to  back.  It  is  principally  used  in  forcing 
substances  apart,  as  when  wedges  are 
used  to  split  wood  and  stones,  or  as 
needles  and  pins  are  used  in  pushing 
apart  the  fibers  of  cloth. 
Axes  and  chisels  and  most 

cutting  tools  except  saws  act  on  the  principle 

of  the  wedge. 

The  Screw.  —  The  screw  is  simply  an  in- 
clined plane  ascending  around  a  central  axis. 
(Figure  145.)  The  projection  of  the  plane 
from  the  axis  is  called  .the  thread.  The 
plane  moves  the  distance  between  the  threads  in  making 
one  turn  around  the  axis.  A  spiral  staircase  is  a  machine 


FIGURE  145 


FIGURE  146 


470       TRANSFERRING  AND   TRANSFORMING  ENERGY 


of  this  kind.  The  screw  is  another  example  of  a  gain  in 
power  with  a  corresponding  loss  in  distance.  The  screw, 
generally  combined  with  the  lever,  is  used  in  many  ordinary 
machines.  The  jackscrew  (Figure  146),  copy-press,  and  vise 
are  examples  of  combinations  of  these  two  simple  machines. 

Man's  Most  Important  Energy  Transformers.  —  Perhaps 
the  first  of  nature's  forces  that  man  made  use  of  was  the 
wind.  He  hoisted  a  sail  for  the  wind  to  strike  upon  and  to 

push  him  from  place 
to  place.  In  about 
the  twelfth  century 
A.D.  he  discovered  a 
way  of  arranging 
sails  upon  a  wheel, 
thus  constructing  a 
windmill  to  help  him 
in  his  work.  The 
windmill  is  still  used 
in  some  places  where 
small  power  is  needed,  but  the  wind  is  no  longer  one  of 
man's  main  sources  of  energy. 

Running  water  early  impressed  man  with  its  power.  He 
finally  harnessed  this  power  for  grinding  his  grain  and  for 
doing  other  kinds  of  work  by  means  of  the  water  wheel. 
Many  shapes  of  wheels  were  tried  before  the  mighty  tur- 
bine, such  as  is  used  at  Niagara  Falls,  was  invented.  It  is 
probable  that  more  power  is  now  developed  at  these  Falls 
than  was  developed  by  all  the  earlier  water  wheels  ever 
used. 

About  the  middle  of  the  eighteenth  century,  a  young 
Scotchman,  James  Watt,  invented  a  machine  to  utilize  the 


AN  A 


NCIENT    bAILBOAl 


MAN'S  IMPORTANT  ENERGY  TRANSFORMERS     471 

power  of  expanding  steam.  He  arranged  a  cylinder  con- 
taining a  piston  so  that  the  steam  would  be  admitted  alter- 
nately on  one  side  and  then  on  the  other  side  of  the  piston. 
As  the  expanding  steam  forces  the  piston  in  one  direction, 
the  used  steam  in  front  of  the  advancing  piston  escapes 
through  an  open  valve.  When  the  piston  reaches  the  end 


A  SIMPLE  WATER  WHEEL  Usi 


K  GRINDING  CORN 


of  its  stroke,  the  moving  valves  cut  off  the  steam  from  the 
one  side  and  allow  it  to  enter  the  other,  thus  driving  the 
piston  back  again  and  forcing  the  used  steam  out  through 
the  escape.  This  continuous  back  and  forth  movement  of 
the  piston  can  best  be  understood  by  an  examination  of  the 
accompanying  diagram.  (Figure  147.) 

In  recent  years  inventors  have  made  it  possible  to  apply 


472       TRANSFERRING  AND   TRANSFORMING   ENERGY 


steam  under  great  pressure  to  a  wheel  somewhat  similar 
in  construction  to  a  water  turbine.  Thus  steam  is  made  to 
give  a  rotary  motion,  instead  of  the  back  and  forth  motion 
of  the  ordinary  steam  engine,  which  must  be  converted  into 
rotary  motion  by  the  connecting  rod  and  crank.  These 
steam  turbines,  as  they  are  called,  have  been  used  to  great 

advantage  in  ocean  ves- 
sels where  there  is  little 
space  available  for  ma- 
chinery and  where  great 
power  and  high  speed 
are  desired. 

In  the  gas  engine  the 
energy  of  gas  exploding 
in  a  cylinder  behind  a 
piston  takes  the  place  of 
expanding  steam  in  driv- 
FIGUBE  147  ing  the  piston.  Usually 

two    or    more    cylinders 

are  used,  and  the  explosions  are  so  timed  that  a  very  steady 
motion  is  given  to  the  shaft.  These  engines  were  first 
made  about  fifty  years  ago  but  have  been  greatly  improved 
recently,  and  are  now  used  very  extensively  for  automobiles, 
motorboats,  and  airplanes. 

The  electric  dynamo  and  the  electric  motor,  which  will 
be  discussed  later,  are  other  energy  transformers  which  man 
has  developed  and  now  constantly  uses. 

Power  Available  to  Man.  —  When  combustion  is  used  as 
a  source  of  energy,  man  is  drawing  upon  his  bank  account 
with  nature,  and  is  using  up  the  stored  energy  of  the  earth. 
But  in  utilizing  the  energy  of  blowing,  wind  and  running 


POWER  AVAILABLE   TO   MAN  473 

water,  he  is  conserving  energy  that  would  otherwise  be 
wasted.  "  The  mill  can  never  grind  again  with  water  that 
is  past."  There  is,  however,  only  so  much  water  power  in 
the  country  and  it  is  exceedingly  important  that  these 


ELECTRIC  POWER  PLANT  AT  NIAGARA 

Conserving  the  energy  of  running  water  by  transforming  it  into  usable 
electrical  energy. 

sources  of  power  should  remain  in  the  possession  of  all  the 
people  as  represented  by  their  Government  and  not  be 
monopolized  for  the  commercial  gain  of  a  few  people.  In 
recent  years  the  United  States  Government  has  arranged  tp 
retain  control  of  power  sites  on  public  land,  and  to  lease 
rather  than  sell  water  power  to  individuals  and  corpora- 
tions. Running  water  is  a  never-stopping,  sun-power 
engine,  and  its  use  should  be  the  birthright  of  mankind. 


474       TRANSFERRING  AND   TRANSFORMING   ENERGY 

SUMMARY 

Man  has  invented  many  simple  and  complex  machines 
for  transferring  and  transforming  energy,  and  has  thus 
simplified  the  doing  of  work.  Among  the  machines  which 
are  used  simply  or  in  complex  combinations  are  the  lever, 
the  wheel  and  axle,  the  pulley,  the  inclined  plane,  the  wedge, 
and  the  screw.  He  has  invented  complex  machines  for 
transforming  the  energy  of  running  water,'  of  burning  fuel, 
and  expanding  steam,  and  of  exploding  gases  into  forms  of 
energy  that  may  be  utilized  at  will.  The  natural  sources  of 
power,  should  never  be  monopolized  for  the  commercial 
gain  of  a  few  people;  they  should  remain  the  birthright  of 
mankind. 

QUESTIONS 

Which  of  the  six  basic  machines  have  you  used?  What  ma- 
chines have  you  seen  that  combined  several  of  these  basic  ma- 
chines ?  Explain  how  they  were  combined. 

In  what  ways  have  you  ever  observed  energy  transformed  by 
machines  so  as  to  do  useful  work? 

What  forces  of  Nature  have  you  ever  seen  used  for  man's  ad- 
vantage? How? 


CHAPTER  XVI 

TWO  BELATED  POEOES   MAN  HAS   HABNESSED  — 
MAGNETISM  AND  ELECTRICITY 

Magnetism.  —  So  much  were  some  of  the  ancients  im- 
pressed with  the  property  of  loadstones  (page  37)  for  attract- 
ing iron  that  one  of  them  suggested  building  a  great  arch 
of  this  material  in  a  temple  so  that  the  iron  statue  of  the 
goddess  would  remain  suspended  in  the  air  without  resting 
upon  any  support.  There  is  an  old  legend  that  the  iron 
coffin  of  Mahomet  rose  and  remained  near  the  ceiling  of  the 
mosque  in  which  it  was  buried. 

Experiment  147.  —  Touch  with  each  end  of  a  bar  magnet  small 
pieces  of  paper,  copper,  zinc,  iron,  sawdust,  and  any  other  materials 
that  may  be  handy.  Which  substances  are  attracted  by  the 
magnet?  Does  it  make  any  difference  which  end  is 
used  ?  Take  a  knife  blade  that  has  no  such  attrac- 
tive power  and  rub  it  several  times  along  one  end 
of  the  magnet ;  then  touch  the  different  substances 
with  it.  Has  it  acquired  any  new  power? 

Experiment  148. —  Suspend  a  bar  magnet  hori- 
zontally in  a  sling  made  from  a  bent  piece  of  wire 
(Figure  148).  Bring  one  of  the  ends  of  another  bar 


magnet  toward  it.    What  is  the  effect  ?    Reverse  the  148 


ends  of  the  magnet  ;  is  there  any  change  in  the  posi- 
tion of  the  suspended  magnet  ?  Bring  a  large,  soft  iron  nail  toward 
either  end  of  the  suspended  magnet.  What  is  the  effect?  Reverse 
the  ends  of  the  nail.  (Be  careful  that  the  nail  has  not  become 
permanently  affected  by  the  magnet.)  Is  the  effect  the  same  as 
when  the  ends  of  the  magnet  were  reversed? 
475 


476  MAGNETISM    AND    ELECTRICITY 

Bring  pieces  of  copper,  zinc,  and  other  substances  toward  the 
magnet.  Do  these  affect  it?  Notice  that  the  ends  of  the  bar 
magnet  are  marked.  What  can  you  state  about  the  attraction  or 
repulsion  of  similar  ends  of  magnets?  Of  opposite  ends?  Does 
it  make  any  difference  in  its  effect  on  the  suspended  magnet 
toward  which  end  the  nail  is  brought  ?  What  substances  do  you 
find  attracted  by  the  magnet  ? 

To  the  end  of  a  small  nail  hanging  by  attraction  to  a  magnet 
bring  another  nail.  How  does  the  first  nail  act  in  respect  to  the 
second  ? 

Experiment  149.  —  Suspend  by  a  string  a  short  bar  magnet  in  a 
sling,  as  in  Experiment  148.  Turn  it  around  in  several  different 
directions.  After  each  change  allow  it  to  come  to  rest  in  whatever 
position  it  will.  Does  it  prefer  any  one  position  to  all  others? 

It  was  early  discovered  that  when  pieces  of  steel  were 
rubbed  on  a  loadstone  they  took  on  the  properties  of  the 
loadstone  and  became  magnets.  In  the  experiments  with 
magnets,  it  was  found  that  like  poles  repelled  and  unlike 
poles  attracted,  and  that  iron  or  steel  in  contact  with  a 
magnet  becomes  magnetized.  Iron  and  steel  are  practi- 
cally the  only  substances  attracted  by  a  magnet,  although 
nickel  and  cobalt  and  a  few  other  substances  have  a 
little  attraction.  Thus  steel  and  iron  are  always  used 
for  magnets. 

The  Magnetic  Field  of  Force.  —  Experiment  150.  — Place  a 

plate  of  window  glass  about  8X 10  inches  above  a  bar  magnet  and 
carefully  sprinkle  iron  filings  over  it.  Describe  the  behavior  of  the 
filings.  Sketch  on  a  piece  of  paper  their  arrangement.  Move  a 
small  compass  about  above  the  glass  plate  and  note  the  directions 
the  needle  assumes.  How  do  the  actions  of  the  needle  and  of  the 
filings  compare  ?  If  feasible  make  a  blue  print  of  the  filings. 

Holding  the  small  compass  two  or  three  inches  above  the  magnet 
move  it  parallel  with  the  magnet  from  end  to  end.  Gently  tap  the 
compass  occasionally  so  that  the  needle  will  move  freely.  How  does 


THE   MAGNETIC  FIELD   OF  FORCE 


477 


the  needle  act  when  it  is  over  the  ends  of  the  magnet  ?  How  does 
the  direction  of  the  compass  needle  compare  with  the  direction  of 
the  bar  magnet  ? 

In  the  experiment  just  performed  we  found  that  when 
iron  filings  were  sprinkled  above  the  magnet  they  arranged 
themselves  in  definite  lines.  The  small  compass  needle  also 
arranged  itself  along  these  lines  when  brought  under  the 
influence  of  the  magnet.  There 
is,  then,  around  a  magnet  a  mag- 
netic field  of  force  which  affects 
magnets  and  magnetic  substances 
brought  within  it.  It  is  found 
that  magnetic  intensity,  like  the 
intensity  of  sound  and  light,  varies 
inversely  as  the  square  of  the 
distance. 

When  the  compass  was  placed 
above  the  ends  of  the  bar  magnet 
one  of  the  ends  of  the  needle  was 
pulled  down  toward  the  magnet, 
or  it  might  be  said  to  dip  toward 
the  magnet.  When  moved  near 
the  middle  of  the  magnet  it  as- 
sumed a  horizontal  position,  and 
when  it  approached  the  opposite  end  of  the  magnet  the 
opposite  end  of  the  needle  dipped.  This  same  action  is 
found  when  a  magnetic  needle  is  carried  from  north  to 
south  upon  the  earth.  If  a  needle  is  carefully  balanced  and 
then  magnetized,  it  will  be  found  no  longer  to  assume  a 
horizontal  position. 

In  the  northern  hemisphere  the  north  end  will  dip  and  in 
the  southern  hemisphere  the  south  end.     In  the  northern 


FIGURE  149 


478  MAGNETISM    AND    ELECTRICITY 

hemisphere  it  is  customary  to  make  the  south  end  of  the 
needle  a  little  heavier  so  that  it  will  stay  in  a  horizontal 
position.  At  the  magnetic  pole  the  needle  would  stand 
vertical.  If  a  needle  is  accurately  balanced  on  a  horizontal 
axis  and  then  magnetized,  it  will  show  the  angle  of  dip  in 
any  locality.  Such  a  needle  is  called  a  dipping  needle 
(Figure  149). 

The  Mariner's  Compass.  —  In  the  ordinary  mariner's 
compass  (Figure  150)  a  magnetic  needle  is  arranged  so  that 
it  will  swing  freely  in  a  horizontal  plane.  A  circular  card  is 
divided  into  four  equal  parts,  the  divid- 
ing lines  of  which  are  marked  with  the 
cardinal  points  of  the  compass,  the  inter- 
vening spaces  being  divided  into  eight 
equal  divisions.  The  card  is  attached  to 
the  needle  and  inclosed  in  a  box  called 
the  binnacle.  This  box  is  arranged  so 
FIGURE  150  that  ^  w^  always  remain  horizontal. 
A  fixed  line  on  the  binnacle  shows  the 
direction  of  the  keel  of  the  ship.  The  card  being  attached 
to  the  needle  always  has  its  "  north  "  pointing  toward  the 
north.  To  determine  the  direction  of  the  ship  it  is  only 
necessary  to  notice  on  the  card  in  what  direction  the  keel 
line  is  pointing.  The  mariner  of  course  must  know  the 
declination  at  the  place  where  he  is  and  make  the  proper 
corrections.  The  different  governments  furnish  tables  and 
charts  showing  these  corrections. 

Theory  of  Magnetism.  —  Experiment  161. —Heat  a  No.  20 
knitting  needle  red  hot  and  plunge  it  quickly  into  cold  water.  This 
tempers  the  needle  so  that  it  will  break  readily.  Magnetize  the 
needle  as  was  done  in  Experiment  8.  When  it  has  become  well 
magnetized,  break  it  in  the  middle.  Test  each  half  with  a  sus- 


THEORY   OF  MAGNETISM  479 

pended  magnet,  as  was  done  in  Experiment  148.  Is  each  half  a 
full  magnet  or  only  half  a  magnet?  Break  these  halves  again  and 
test.  What  effect  does  breaking  a  magnet  have  upon  the  magnet  ? 

In  Experiment  151  it  was  found  that  if  a  magnet  is  broken 
in  two,  each  half  is  a  perfect  magnet.  If  these  halves  are 
broken,  each  piece  is  a  perfect  magnet,  and  so  on  as  long 
as  the  division  is  kept  up.  It  is  also  found  that  if  a  magnet 
is  heated  or  suddenly  jarred  or  pounded  it  loses  its  magnet- 
ism. If  a  magnet  is  filed  into  filings  and  these  filings  are 
put  into  a  glass  tube,  the  tube  will  have  no  magnetic  prop- 
erties but  will  act  to  a  magnet  like  an  ordinary 
iron  bar. 

If  now  the  tube  is  held  vertically  and  tapped 
several  times  on  a  strong  magnet,  the  tube  will 
be  found  to  have  acquired  the  properties  of  a 
magnet.  The  tapping  joggled  the  particles  so 
that  they  could  arrange  themselves  under  the 
influence  of  the  magnetic  pole  and  when  they  be- 
came so  arranged  a  magnet  was  the  result.  If  the 
filings  are  now  poured  out  of  the  tube  and  then 
put  back  again,  there  will  be  no  magnetization.  F 

It  was  the  arrangement  of  the  tiny  magnetized  particles 
which  must  have  caused  the  contents  of  the  tube  to  be- 
come magnetic.  It  would  therefore  seem  probable  that 
magnetism  must  be  a  property  of  the  exceedingly  small 
particles  or  molecules  of  which  the  iron  or  steel  as  well  as 
all  other  substances  are  supposed  to  be  composed. 

It  is  supposed  that  when  a  bar  of  steel  becomes  magnet- 
ized the  molecules  arrange  themselves  in  definite  directions, 
as  do  the  filings  in  the  tube.  The  molecules  of  magnetic 
substances  are  supposed  to  be  separate  little  magnets.  In 
the  unmagnetized  bar  (Figure  151)  their  poles  point  in  all 


480  MAGNETISM    AND    ELECTRICITY 

directions,  dependent  upon  their  mutual  attraction ;  and  thus 
they  neutralize  one  another.  When  the  bar  becomes  mag- 
netized the  molecules  tend  to  arrange  themselves  so  that 
like  poles  lie  in  the  same  direction  (Figure 
152).  When  the  magnet  is  heated  or  jarred  the 
molecules  are  moved  out  of  this  alignment  and 
the  magnetism  is  weakened. 

Electricity  by  Friction.  —  It  was  known  by  the 
ancient  Greeks  that  when  certain  substances, 
one  of  which  was  amber,  were  rubbed,  they 
had  the  power  of  attracting  light  objects.  This 
property  was  afterward  called  electricity,  from 
FIGURE  152  the  Greek  word  for  amber. 

Experiment  152.  —  Place  some  small  pieces  of  paper  or  pith  balls 
on  a  table  and  after  rubbing  a  glass  rod  with  silk  bring  it  near  the 
pieces.  Do  the  same  with  a  stick  of  sealing  wax  or  a  hard  rubber 
rod  rubbed  with  flannel  or  a  cat's  skin.  Note  the  action  of  the 


BBBE 
BBBE 
BGBB 
BBBH 
BBBB 
BBBB 
BHHH 
BBBB 
BBBB 
BBBB 
BBBB 
BBBB 
HBBB 


Experiment  153.  —  Rub  a  glass  rod  briskly  with  silk  and  place  in 
a  wire  sling  such  as  was  used  in  Experiment  148.  Bring  toward  one 
end  of  the  glass  rod  another  glass  rod  which  has  been  rubbed  with 
silk.  Do  the  rods  attract  or  repel  each  other?  Bring  toward  the 
suspended  rod  a  piece  of  sealing  wax  or  a  vulcanite  rod  which  has 
been  rubbed  with  flannel  or  a  cat's  skin.  Does  this  repel  or  at- 
tract the  glass  rod? 

Experiment  154.  —  Suspend  a  pith  ball  by  a  silk  thread  from  the 
ring  of  a  ringstand.  Rub  a  glass  rod  with  a  piece  of  silk  and  bring 
it  near  the  pith  ball  but  do  not  allow  the  two  to  touch.  Note  the 
action  of  the  ball.  Touch  the  pith  ball  with  the  rod.  Does  it 
behave  now  as  it  did  before?  Rub  a  vulcanite  rod  with  a  piece  of 
flannel  or  cat's  skin  and  bring  it  near  a  suspended  pith  ball.  Does 
the  pith  ball  act  as  it  did  with  the  glass  rod  ?  Touch  the  pith  ball 
with  the  rod.  How  does  it  act?  Bring  a  glass  rod  rubbed  with 
silk  near  a  pith  ball  which  has  been  in  contact  with  a  vulcanite  rod 


ELECTRICITY   BY   FRICTION 


481 


after  it  was  rubbed  with  flannel  or  a  cat's  skin.     Does  the  glass  rod 
repel  or  attract  the  ball? 

Experiment  156.  —  Suspend  a  pith  ball  from  the  ring  of  a  ring- 
stand  by  a  very  fine  piece  of  copper  wire  no  larger  than  a  thread. 
Wrap  the  wire  around  the  pith  ball  in  several  directions.  Bring  a 
rubbed  glass  rod  toward  the  pith  ball.  Does  it  act  as  it  did  when 
suspended  by  silk?  Allow  the  ball  to  touch  the  rod.  Does  the 
ball  now  act  as  it  did  when  suspended  by  silk?  Try  these  same 
experiments,  using  the  vulcanite  rod. 

From  the  previous  experiments  it  has  been  seen  that 
when  glass  is  rubbed  with  silk,  and  vulcanite  with  flannel 


FIGURE  153 

or  a  cat's  skin,  they  seem  to  have  two  different  kinds  of 
electrical  charges.  The  like  kinds  repel  each  other  and  the 
opposite  kinds  attract.  These  two  kinds  are  called  posi- 
tive and  negative  respectively. 

Whether  there  are  really  two  kinds  of  electricity  has  not 
yet  been  fully  determined,  but  electricity  acts  exactly  MS  it 
would  if  there  were  two  kinds,  and  it  has  become  customary 


482  MAGNETISM    AND    ELECTRICITY 

to  speak  as  if  there  were.  In  Experiment  154  it  was  found 
that  pith  balls  suspended  by  a  silk  thread  could  be  charged 
with  electricity  if  brought  in  contact  with  a  charged  body. 
Experiment  155  showed  that  this  was  not  possible  when 
they  were  suspended  by  a  copper  wire.  The  wire  conducted 
the  electricity  away.  Substances  like  copper  that  conduct 
electricity  are  called  conductors,  and  those  substances  like 
silk  which  will  not  conduct  it,  non-conductors. 


A  FLASH  OF  LIGHTNING 

Experiment  156.  —  Having  started  the  electrical  action  in  a  static 
electrical  machine  (Figure  153),  pull  the  knobs  as  far  apart  as  the 
spark  will  jump  and  notice  the  course  taken  by  the  spark.  Does  it 
travel  in  a  straight  line?  Hold  a  piece  of  cardboard  between  the 
knobs  so  that  its  edge  is  just  within  the  line  joining  them.  What  ef- 
fect does  the  cardboard  have  upon  the  direction  taken  by  the  spark? 
Place  the  cardboard  so  that  it  entirely  covers  one  of  the  knobs. 
Is  the  spark  able  to  pass  through  the  card?  Attach  a  wire  with  a 
sharp  point  to  each  of  the  knobs  and  extend  it  vertically  two  or 
three  inches  above  the  knob.  Start  the  machine.  Do  sparks 


ELECTRICITY  BY   FRICTION 


483 


now  jump  across  between  the  knobs?  Why  are  houses  provided 
with  lightning  rods? 

About  the  middle  of  the  eighteenth  century,  Benjamin 
Franklin  proved  by  his  notable  kite  experiment  that  light- 
ning was  simply  an  electrical  discharge  between  the  clouds 
and  the  earth,  or  be- 
tween different  clouds. 
This  discharge  is  simi- 
lar to  that  which  takes 
place  on  an  electrical 
machine.  The  elec- 
tricity in  the  clouds 
attracts  as  close  as 
possible  the  opposite 
kind  of  electricity  on 
the  earth's  surface  and 
tends  to  hold  it  ac- 
cumulated on  high 
objects.  If  the  attrac- 
tion is  sufficient,  the 
electricity  discharges 
between  the  cloud  and 
the  object,  and  we  say 
the  object  was  struck 
by  lightning. 

If    a    sharp    point, 
such    as    a    lightning 

rod,  is  present  on  the  object  where  the  electricity  tends 
to  accumulate,  it  allows  the  electricity  to  pass  off  gradually 
before  enough  accumulates  to  cause  damage.  Lightning 
rods,  however,  must  be  continuous  conductors  and  properly 
terminated  in  the  ground. 


A  TREE  COMPLETELY  SHATTERED  BY  A 
STROKE  OF  LIGHTNING 


484  MAGNETISM    AND    ELECTRICITY 

Serviceable  Electrical  Energy.  —  In  Experiments  152  to 
156,  muscular  energy  was  transformed  into  electrical  energy. 
In  none  of  these  cases,  however,  could  the  electrical  energy 
have  been  made  of  practical  service  to  man.  Methods 
of  producing  electrical  energy  under  different  conditions  had 
to  be  found  before  this  form  of  energy  could  be  made  to  do 
work.  Within  recent  years  man  has  done  this  and  has  thus 
added  electricity  to  the  forms  of  energy  he  is  able  to  con- 
trol for  his  service. 

Current  Electricity.  —  In  Experiment  155  it  was  found 
that  it  was  impossible  to  charge  the  pith  ball  when  it  was 
suspended  by  the  copper  wire.  The  electricity  passed  off, 
*^?«~c^  was  conducted  away,  through  the  wire. 

We  had  here  a  current  of  electricity 
through  the  wire,  but  it  was  only  for 
an  instant.  At  the  opening  of  the 
nineteenth  century,  an  Italian  by  the 
name  of  Volta  discovered  how  a  con- 
tinuous electric  current  could  be  pro- 
duced. If  a  strip  of  zinc  and  a  strip  of 
copper  or  carbon  are  placed  in  dilute 
sulphuric  acid  and  connected  with  a  wire  (Figure  154),  a 
current  of  electricity  will  flow  through  the  wire  from  the 
copper  or  carbon  to  the  zinc.  The  current  is  due  to  the 
chemical  action  of  the  sulphuric  acid  on  the  zinc.  Chemical 
energy  has  been  transformed  into  electrical  energy. 

An  arrangement  such  as  that  shown  in  Figure  154  is 
called  a  voltaic  cell,  after  its  discoverer.  In  a  cell  of  this  kind, 
hydrogen  bubbles  formed  by  the  action  of  the  acid  on  the 
zinc  (see  Experiment  56)  soon  collect  on  the  copper  strip, 
and  the  current  weakens  and  finally  stops.  The  cell  is 


CURRENT   ELECTRICITY  485 

then  said  to  be  polarized.  If  cells  are  to  be  of  practical 
value,  they  must  not  quickly  polarize ;  that  is,  a  way  must 
be  found  to  get  rid  of  the  hydrogen  bubbles.  This  is  gen- 
erally done  by  putting  some  substance  into  the  cell  that  will 
unite  with  the  hydrogen  and  thus  keep  the  copper  strip  free 
of  hydrogen  bubbles.  Many  kinds  of  cells  have  been  in- 
vented which  do  not  readily  polarize. 

The  so-called  dry  cell  (Figure  155)  is  most  used  at  the 
present  time.  It  consists  of  a  zinc  can  lined  on  the  inside 
with  porous  paper.  In  the  center  is  a  carbon  rod.  Packed 
around  the  carbon  and  filling  the  can  is  usually 
a  moist  mixture  of  sal  ammoniac,  manganese 
dioxide,  granulated  carbon,  plaster  of  Paris,  and 
generally  small  quantities  of  other  materials.  In 
this  cell  the  sal  ammoniac  acts  upon  the  zinc 

somewhat  as  the  sulphuric  acid  did  in  the  simple 

n   /?     j.  ^-111  1-1      FIGURE  155 

cell  first  mentioned,  and  the  manganese  dioxide 

unites  chemically  with  the  hydrogen  bubbles  and  thus  re- 
moves them  from  the  carbon  rod.  The  plaster  of  Paris 
keeps  the  cell  in  rigid  shape  and  the  granulated  carbon 
helps  to  keep  the  contents  porous  so  that  action  may  go  on 
freely  within  the  cell. 

In  voltaic  cells  the  copper  or  carbon  strip  is  called  the 
positive  electrode  or  pole,  and  the  zinc  is  called  the  negative 
electrode  or  pole. 

Experiment  167.  —  Connect  a  positive  and  a  negative  pole  of  two 
dry  cells  by  a  fairly  heavy  copper  wire.  Attach  a  similar  piece  of 
wire  to  each  of  the  other  poles  and  connect  these  pieces  by  means 
of  a  short,  very  fine,  iron  wire.  (Figure  156.)  The  iron  wire  will 
become  red  hot.  Now  remove  the  fine  iron  wire  and  connect  the 
loose  ends  of  the  copper  wires  to  the  socket  of  a  small  one  or  two 
candle  power  electric  light,  such  as  is  often  used  to  illuminate  the 


486 


MAGNETISM    AND    ELECTRICITY 


FIGURE  156 


speedometer  of  an  automobile.     (Figure  157.)     The  light  is  made 
to  glow. 

In  the  preceding  experiment  we  found  that  electrical 
energy,  in  overcoming  the  resistance  of  the  iron  wire,  was 
changed  into  heat.  When  a 
current  of  electricity  passes 
through  any  substance,  the  sub- 
stance offers  resistance  to  it. 
The  amount  of  resistance  offered 
by  a  conductor  varies  with  the 
kind  of  material,  its  length  and 
its  thickness.  Heating  due  to 
resistance  of  an  electric  current  is  utilized  in 
the  construction  of  electric  flatirons,  toasters, 
stoves,  and  other  devices.  The  electricity  is 
generally  conducted  to  the  utensils  through  a 
wire  made  up  of  a  number  of  small  copper  wires, 
covered  with  non-conducting  materials.  The 
resistance  of  the  connecting  cord  is  very  low. 

From  this  cord,  the  current 
passes  through  coils  in  the 
utensil  that  offer  high  re- 
sistance. These  are  so  ar- 
ranged that  the  resulting 
heat  is  delivered  with  al- 
most no  loss  to  the  surface 
which  is  to  be  heated.  Al- 
though it  costs  more  to 
produce  the  same  amount 
of  heat  by  electricity  than 
it  does  by  the  other  methods  usually  employed  in  the  home, 
yet  for  many  purposes  this  heat  can  be  applied  with  so 


FIGURE  157 


ELECTRIC  IRON  SHOWING  HEATING 
ELEMENT  (E) 


ELECTRIC  LIGHTING 


487 


URE    158 


little  loss  that  the  use  of  electricity  in  some  kinds  of  heating 
becomes  not  only  convenient  but  also  really  economical. 

Heat  generated  by  electricity  is  also 
used  for  welding  (Figure  158),  and  is 
beginning  to  replace  the  forge.  If  metal 
rods  are  pressed  together  end  to  end  and ' 
a  sufficiently  great  current  of  electricity 
is  sent  through  them,  the  heat  generated 
at  the  point  of  contact,  where  the  resist- 
ance is  greatest,  will  be  sufficient  to  weld 
them  together.  The  rails  of  car  tracks 
are  often  welded  together  in  this  way. 
Wherever  electricity  is  received  from  wires  in  which  the 
strength  of  the  current  may  vary  considerably 
from  time  to  time,  it  is  necessary  to  protect 
electrical  appliances  from  the  heat  caused  by 
too  great  a  current.  This  is  done  by  inserting 
in  the  circuit  a  wire  which  will  melt  if  too 
much  current  passes  through  it,  and  will  thus 
instantly  break  the  circuit.  Such  a  safety  de- 
vice is  called  a  fuse.  (Figure  159.) 

Electric  Lighting.  —  The  little  electric  lamp 
used  in  Experiment  157,  like  most  other  in- 
candescent lamps,  consists  of  a  thread  or  fila- 
ment of  carbon  inclosed  in  a  glass  bulb  from 
which  the  air  has  been  exhausted.  When  this 
lamp  is  connected  with  an  electric  current  the 
carbon  is  heated  white  hot  by  the  resistance  it 
offers  to  the  electric  current.  The  carbon  cannot  burn  be- 
cause there  is  no  air  in  the  bulb,  and  it  does  not  melt  since 
there  is  not  sufficient  heat  to  accomplish  this.  Incandescent 


FIGURE  159 


488  MAGNETISM    AND    ELECTRICITY 

lamps  are  also  made  with  metal  filaments.  Only  two 
metals,  tantalum  and  tungsten,  have  been  found  that  will 
withstand  the  intense  heat.  Incandescent  lamp  filaments 
made  from  these  metals  are  necessarily  much  longer  and 
thinner  than  the  carbon  filaments,  and  are  therefore  more 
easily  broken.  But  their  great  advantage  lies  in  the  fact 
that  they  use  only  about  one  third  the  amount  of  current 
in  giving  the  same  light.  A  tungsten  filament  will  with- 
stand much  heavier  jarring  when  it  is  hot  than  when  cold. 
It  sometimes  happens  that  a  lamp  has  imperfections  that 
render  it  dangerous  to  handle  carelessly.  If  one  touches 
the  metal  part  of  such  a  lamp  when  it  is  in  use,  especially 
with  wet  hands,  one  is  likely  to  receive  a  severe  shock.  These 
shocks  have  sometimes  proved  fatal.  To  avoid  such  possible 
danger  one  should  touch  only  the  hard-rubber  switch  in 
turning  a  light  on  or  off.  Especial  care  should  be  taken 
when  the  hands  are  wet,  because  moisture  is  an  excellent  con- 
ductor of  an  electrical  current. 

Electroplating.  —  Experiment  168.— Almost  fill  a  dish  with  a 
strong  solution  of  copper  sulphate  (blue  vitriol).     Across  the  dish 

and  a  little  distance  apart, 
place  two  parallel  wooden 
rods.  Carefully  clean  with 
fine  sandpaper  a  strip  of  lead 
and  a  strip  of  copper.  Punch 
a  hole  in  an  end  of  each  strip 
and  attach  to  each  strip  two 

or  three  feet  of  fairly  heavy 

SIMPLE  APPARATUS  FOB  ELECTROPLATING  ,  tf        .    J 

copper  wire .    Pinch  the  wires 

firmly  on  to  the  copper  and  lead  at  the  points  of  connection.  Sus- 
pend a  strip  from  each  of  the  rods  by  winding  the  wire  once  around 
the  rod.  Attach  the  wire  from  the  copper  to  the  positive  pole  of  a 
battery  and  the  wire  from  the  lead  to  the  negative  pole.  A  copper 
plate  will  be  deposited  on  the  lead. 


ELECTROPLATING 


489 


In  the  preceding  experiment  the  copper  solution  is  de- 
composed by  the  electric  current  as  it  passes  through  the 
solution  from  the  copper  strip  to  the  lead  strip,  and  the 
copper  freed  from 
the  compound  is  de- 
posited on  the  lead. 
Just  as  fast  as  cop- 
per from  the  solution 
is  deposited  on  the 
lead  strip,  the  same 
amount  of  copper  is 
dissolved  from  the 
copper  strip ;  and  so 
the  strength  of  the 
solution  is  main- 
tained as  long  as 
there  is  any  of  the 
copper  strip  remain- 
ing. If  it  were  de- 
sired to  plate  with 
silver,  a  silver  strip 
would  have  to  be 
substituted  for  the 
copper  strip  and  a 
solution  of  a  suitable 

silver  compound  Sub-  AN  ELECTROTYPE 

Stituted  for  the  COP-        Phot°SraPh  of  the  plate  from  which  page  15 

of  this  book  is  printed. 

per  sulphate  solution. 

Whatever  the  metal  used  for  plating,  corresponding  solutions 
would  have  to  be  used.     All  gold,  silver,  nickel,  and  other 
plating  is  done  in  this  way. 
This  book,  like  all    books  made  in  large   numbers,    has 


490  MAGNETISM    AND    ELECTRICITY 

been  printed  from  electrotype  plates.  First  a  page  was 
'set  up  in  type,  and  then  a  careful  impression  of  it  was  taken 
in  wax.  Wax  is  not  a  good  conductor  of  electricity  and  so 
the  face  of  the  wax  mold  was  evenly  and  thinly  coated 
with  graphite  in  order  to  make  it  conduct  electricity.  The 
graphite-covered  mold  was  then  attached  to  the  nega- 
tive electric  pole,  as  was  the  lead  in  Experiment  158,  and 
immersed  in  the  copper  sulphate  solution.  To  the  positive 
pole  was  attached  a  copper  strip.  As  soon  as  a  layer  of 
copper  of  the  thickness,  of  a  calling-card  had  been  deposited 
on  the  mold,  taking  its  shape,  the  newly  formed  copper 
plate  was  separated  from  the  wax  impression  and  was 
"  backed  up  "  with  type  metal  to  make  it  strong  enough 
to  be  used  in  the  printing  press. 

Electromagnet.  —  Experiment  169.  —  Wind  several  feet  of  No. 
20  insulated  copper  wire  around  the  nail  used  in  Experiment  148  as 
you  would  wind  thread  on  a  spool.  Attach  the  ends  of  this  wire 

to  the  poles  of  a  dry  cell. 
Brin8  the  nail  thus  arranged 
toward  a  suspended  magnet. 
Reverse  the  ends  of  the  nail. 
Does  the  nail  act  as  it  did 
before  it  was  placed  within 
the  coil  of  wire  connected  to 
the  battery?  Bring  another 
nail  in  contact  with  its  ends. 

FIGUBK  160  What  happens?    What  has 

the  nail  as  arranged  be- 
come? Disconnect  one  of  the  wires  from  the  battery  and  try 
the  test  again.  Does  the  nail  act  as  it  did  when  the  battery 
was  connected? 

We  found  that  if  a  nail  is  placed  in  a  coil  of  wire  connected 
with  an  electric  battery  (Figure  160)  it  becomes  magnetic, 
but  only  as  long  as  the  connection  is  maintained.  Magnets 


THE   ELECTRIC   BELL 


491 


of  this  kind  are  called  electromagnets.  If  the  nail  had  been 
hard  steel  and  the  battery  exceedingly  strong,  the  steel  would 
have  remained  a  magnet  after  being  taken  out  of  the  coil. 
Electromagnets  have  come  to  be  of  almost  inestimable 
use  in  modern  life.  The  telegraph,  the  telephone,  the  mag- 
netic crane,  the  electric  motor,  and  almost  innumerable 


Courtesy  of  IMnoit  Central  KaUroaa 
ELECTROMAGNETIC  CRANE 

Loading  steel  rails  on  a  freight  car.     The  magnet  is  lifting  seven  rails,  a 
burden  of  about  three  and  one  half  tons  of  steel. 

other  mechanical  devices  are  dependent  largely  upon  the 
principle  of  electromagnetism  for  their  usefulness. 

The  Electric  Bell.  —  One  of  the  simplest  applications  of 
the  electromagnet  is  the  electric  bell  (Figure  161).  When 
the  punch-button  (P)  is  pushed  down  it  closes  the  circuit 
through  the  electromagnet  (M).  The  hammer  (H)  is  then 


492 


MAGNETISM    AND    ELECTRICITY 


FIGURE  161. — ELECTRIC  BELL 


attracted  toward  the 
magnet,  and  as  it 
moves  toward  it  the 
circuit  is  broken  at 
(C).  Because  of  this 
break  the  current  no 
longer  flows  through 
(M)  and  the  soft  iron 
cores  instantly  lose 
their  magnetic  power. 
Since  the  hammer  is 
no  longer  attracted 
to  (M),  it  is  thrown 
back  by  the  spring  (S)  to  its  original  position,  thus  closing 
the  circuit  again  and  reestablishing  magnetic  attraction 
at  (M).  This  alternate 
closing  and  breaking  of 
the  circuit  at  (C)  goes 
on  so  rapidly  that  the 
successive  taps  of  the 
clapper  on  the  bell  blur 
into  an  almost  continu- 
ous sound.  As  soon  as 
the  button  (P)  is  re- 
leased, the  circuit  is  broken  at  that  point  and  the  bell 
ceases  ringing. 

The  Electric  Telegraph.  —  In 
1832  an  American,  Samuel  F.  B. 
Morse,  invented  the  commercial 
telegraph.  This  was  the  first  step 
in  the  wonderful  progress  that  has 
FIGURE  163  been  made  during  the  last  century 


FIGURE  162 


ELECTRICAL  COMMUNICATION 


493 


UNE  BATTERY 
FIGURE  164 


in  communicating  rapidly  between  distant  points.  The 
necessary  instruments  used  in  this  form  of  communication 
are  a*  sounder  (Figure  162)  and  a  key  (Figure  163).  The 
following  experiment  illustrates  the  ar- 
rangement  and  operation  of  a  simple 
telegraph. 

Electrical  Communication. — Experiment 
160.  —  Attach  one  end  of  a  wire  to  a  pole  of  a 
dry  cell  and  the  other  end  to  one  of  the  bind- 
ing posts  of  a  telegraphic  sounder.  From  the 
other  binding  post  of  the  sounder  lead  a  wire 
to  a  binding  post  of  a  telegraphic  key.  Con- 
nect the  free  binding  post  of  the  key  with  the 
free  pole  of  the  battery  (Figure  164).  When 
the  key  is  pushed  down,  the  circuit  is  closed 
and  the  sounder  clicks.  If  a  relay  can  be  procured,  remove  the 
sounder  and  connect  two  of  the  binding  posts  of  the  relay  in  the 
same  way  that  the  sounder  was  connected. 

Connect  one  of  the  free  binding  posts  of  the  relay  with  a  binding 
post  of  the  sounder  and  the  other  binding1  post  with  the  pole  of  a 
dry  cell.  Connect  the  other  pole  of  the  dry  cell  with  the  free 
binding  post  of  the  sounder.  When  the  key  closes  the  circuit 

through  the  relay, 
the  circuit  through 
the  sounder  and  its 
dry  cell  is  closed 
by  the  relay  (Fig- 
ure  165),  and  the 
sounder  clicks.  This 
is  the  usual  arrange- 
ment in  a  simple 
telegraph  office.  The  sounder  in  the  first  part  of  the  above  experi- 
ment can  be  replaced  by  an  electric  bell  (Figure  166)  and  (he- 
key  by  a  push  button,  thus  showing  the  arrangement  of  the 
ordinary  doorbell. 


FIGURE  165 


494  MAGNETISM    AND    ELECTRICITY 

The  sounder  is  simply  an  electromagnet  such  as  was  made 
in  Experiment  159,  arranged  to  attract  a  piece  of  soft  iron 
held  at  a  short  distance  from  it  by  a  spring.  When  this 

piece  of  iron  is  attracted 
toward  the  magnet,  it 
strikes  on  another  piece 
of  iron,  making  a  click, 
and  so  remains  drawn 
to  the  magnet  as  long 
as  the  circuit  is  kept 
closed.  Thus  long  and 

FIGURE  166  ... 

short  clicks  can  be  made. 

Morse  arranged  a  combination  of  these  long  and  short 
clicks  to  represent  .the  alphabet.  Thus  he  was  able  to 
send  words  from  one  station  to  another. 


WIRELESS  TELEGRAPH  STATION,  Los  ANGELES 

Many  improvements  have  been  made  since  Morse  first 
sent  a  dispatch  between  Washington  and  Baltimore,  but 
his  dot-and-dash  alphabet  and  the  electromagnet  sounder 
and  the  key  are  still  in  use.  Since  1832,  the  land  has  been 


THE  TELEPHONE  495 

strung  with  telegraph  wires  and  the  ocean  girdled  with 
cables,  and  now  an  important  event  occurring  in  any  part 
of  the  earth  is  known  almost  instantly  in  all  other  parts. 
The  telephone,  the  wireless  telegraph,  and  the  wireless 
telephone,  all  electrical  devices,  have  added  to  the  ease  of 
communication  so  that  the  whole  earth  is  brought  into  such 
close  relation  that  every  part  knows  what  all  the  other  parts 
are  doing. 

The  Greatest  Electrical  Discovery.  —  In  1831,  Michael 
Faraday,  an  English  physicist,  made  a  discovery  the  results 
of  which  have  almost  revolu- 
tionized civilized  man's  in- 
dustrial life.  He  found  that 
when  a  magnet  is  quickly 
thrust  into  a  coil  of  wire  a  FlGURE  167 

momentary  electrical  current  is  generated  in  the  wire,  and 
when  the  magnet  is  removed  a  momentary  current  is  gener- 
ated in  the  o;>/>o.v//r  direction.  The  same  effect  is  produced 
if  the  strength  of  the  magnet  in  the  coil  is  quickly  increased 
or  decreased,  or  if  the  coil  is  revolved  between  the  poles 
of  a  magnet.  This  discovery  makes  it  possible  to  transform 
mechanical  energy  into  electrical  energy  and  i>  n-.-ponsible 
for  the  invention  of  the  dynamo,  the  motor,  and  many 
other  electrical  devices. 

The  Telephone.  —  In  1875  Alexander  Graham  Bell  first 
communicated  by  telephone  from  Boston  to  Cambridge,  a 
distance  of  only  a  few  miles.  To-day  man  can  talk  across 
the  continent.  Probably  no  device  has  resulted  in  greater 
saving  of  time. 

The  simple  telephone  (Figure  168)  consists  of  a  hard- 
rubber  case  in  which  is  a  permanent  bar  magnet  surrounded 


496 


MAGNETISM    AND    ELECTRICITY 


at  the  end  by  a  coil  of  fine  wire.  In  front  of  the  magnet, 
and  almost  touching  it,  is  mounted  a  thin  iron  disk.  Above 
this  a  concave  rubber  cap  with  a  hole  in  the  center  com- 
pletes the  case.  The  ends  of  the  coil  of  wire  are 
connected  with  the  wires  from  the  coil  of  another 
instrument  of  the  same  kind.  One  of  the  wires 
from  each  coil  may  be  connected  with  the  ground. 
The  sound  waves  from  the  voice  (or  from  any 
other  source)  cause  the  disk  to  vibrate  back  and 
forth  in  front  of  the  magnet.  These  rapid  vibra- 
tions of  the  disk  result  in  correspondingly  rapid 
changes  in  the  strength  of  the  magnet,  and  momentary 
electrical  currents  are  induced  in  the  coil  of  wire.  These 
electrical  impulses  flow,  to  the  coil  of  wire  in  the  other 
instrument,  where  they  cause  correspondingly  rapid  changes 


FIGURE  168 


U.  S.OfflCtOt 

TELEPHONE  STATION  IN  THE  TRENCHES  DURING  THE  WORLD  WAR 


.    THE   DYNAMO 


497 


FIGURE  169 


in  the  strength  of  the  permanent  bar  magnet  of  that 
instrument.  The  rapid  variations  of  strength  of  this  mag- 
net cause  the  disk  in  front  of  it  to  vibrate  in  the 
same  way  that  the  first  disk  vibrated  and  thus  to  throw 
out  sound  waves  similar  to  those  of  the 
speaker's  voice.  The  sound  is  in  no  sense 
transmitted.  The  sound  waves  are  trans- 
formed into  electrical  impulses  which  are 
transmitted  to  the  other  instrument,  where 
they  are  again  transformed  into  sound  waves. 

For  complicated  modern  telephone  systems,  a  different 
instrument  is  used  for  transmitting  (Figure  169),  but  the 
principle  involved  is  the  same.  The  instrument  described 

is  still  used  for  re- 
ceiving, except  that 
the  bar  magnet  has 
been  replaced  by  a 
U-shaped  magnet. 

The  Dynamo.  — 
The  dynamo  is  a  pro- 
foundly important 
result  of  Faraday's 
discovery.  In  the 
dynamo,  coils  of  wire 
are  revolved  between 
strong  magnetic 
poles,  and  the  cur- 
rents of  electricity 
which  are  generated  are  collected  and  delivered  to  the  line 
wire  to  be  used  wherever  desired.  In  commercial  machines, 
there  are  usually  several  pairs  of  electromagnets  and  many 


DYNAMO 


498 


MAGNETISM    AND    ELECTRICITY 


coils  of  wire.     The  coils  are  revolved  by  means  of  water 
power,  steam  power,  or  any  other  available  power. 

The  electricity  that  is  generated  by  the  dynamo  is  easily 
transferred  by  wires  to  a  long  distance  from  the  'point  where 
it  is  generated.  Los  Angeles  uses  electrical  power  which  is 
generated  in  the  mountains  over  300  miles  away.  The 


Courtesy  of  Chicago,  Milwaukee  and  St.  Paul  Railway 

POWER  PLANT  AND  DAM  OF  THE  MONTANA  POWER  COMPANY 

This  plant  at  Great  Falls,  Montana,  transforms  energy  of  running  water  into 

electrical  energy  by  which  trains  are  operated  over  641  miles  of  track. 

energy  of  the  water  falling  at  Niagara  is  transformed  into 
electrical  energy  which  is  utilized  for  transportation  and 
for  industrial  purposes  at  a  distance  of  nearly  200  miles. 
The  location  of  the  power  no  longer  determines  the  site  of  a 
factory.  The  factory  may  be  located  at  the  most  con- 
venient place  possible  and  be  run  by  power  which  is  trans- 
mitted from  almost  inaccessible  mountain  retreats. 


THE   ELECTRIC  MOTOR 


499 


The  Electric  Motor.  —  In  the  dynamo  the  coils  of  wire 
are  revolved  in  a  magnetic  field  by  some  mechanical  power, 
and  electricity  is  generated  in  the  coils.  In  the  motor  the 
process  is  reversed ;  electricity  is  passed  through  the  coils  of 
the  motor.  This  causes  them  to  revolve  in  a  magnetic 
field  and  to  produce  mechanical  power.  In  appearance  and 


Courtesu  of  Chicago,  Afllwautee  and  St.  Paul  Railway 
ELECTRIC  LOCOMOTIVE 

One  of  the  locomotives  which  obtains  its  power  from  the  plant  pictured 
opposite.     The  most  powerful  electric  locomotive  in  the  world. 

make-up  the  two  machines  are  similar,  but  their  work  is 
different.  The  dynamo  generates  an  electrical  current ;  the 
motor  uses  an  electrical  current. 

In  the  running  of  the  ordinary  street  car,  the  motor  and 
the  dynamo  supplement  each  other.  At  the  power  house 
are  dynamos  run  by  any  convenient  kind  of  mechanical 
power.  The  electricity  that  is  generated  is  collected  and 


500  MAGNETISM    AND    ELECTRICITY 

transmitted  by  wires  and  trolley  through  the  controller 
to  the  motor  under  the  street  car.  The  motorman,  by 
means  of  the  controller,  is  able  to  turn  the  current  into  the 
motor  or  to  shut  it  off.  When  the  current  is  turned  on, 
the  motor  revolves ;  by  gearings  the  motion  is  imparted  to 
the  wheels  and  the  car  moves.  Thus  the  electricity  gen- 
erated by  the  dynamos  in  power  houses,  wherever  they 
may  be,  not  only  lights  our  homes  and  streets,  but  also  en- 
ables the  little  motors  in  our  homes,  the  powerful  motors 
on  street  cars,  and  the  giant  motors  of  our  factories  to  do 
all  kinds  of  work  for  us. 

Theory  of  Electricity.  —  A  great  deal  is  known  about  how 
electricity  acts  and  what  it  does,  but  as  yet  little  is  known 
about  what  it  really  is.  Recent  experiments  indicate  that 
the  atoms  of  matter  (page  51)  contain  electricity,  and 
that  the  negative  electricity  in  them  exists  in  the  form 
of  exceedingly  minute  particles  called  electrons.  There 
are  hundreds  of  these  electrons  in  each  atom,  and  they  are 
held  there  probably  by  the  attraction  of  a  positive  charge 
of  electricity  at  the  center  of  the  atom.  If  the  positive  and 
negative  charges  in  the  atoms  of  a  body  are  equal,  the  body 
is  unelectrified. 

If,  however,  the  electrons  are  in  any  way  joggled  off  and 
accumulated,  a  negative  charge  of  electricity  develops 
where  this  accumulation  takes  place.  As  the  electrons  are 
all  negative,  they  repel  one  another  and  tend  to  move  away 
from  the  point  where  they  have  accumulated  to  places 
where  the  accumulation  is  not  so  great.  This  is  what  hap- 
pened in  Experiment  156,  when  the  electrical  machine  was 
used.  An  electric  current  is  supposed  to  be  a  stream  of 
these  electrons. 


QUESTIONS  501 

SUMMARY  * 

Certain  substances  may  be  made  to  take  on  the  properties 
of  loadstone  and  to  become  magnets.  A  magnet  has  a 
positive  and  a  negative  pole.  The  dipping  needle  and  the 
mariner's  compass  are  applications  of  magnetic  properties. 

There  are  two  kinds  of  electrical  charges,  positive  and 
negative.  Electricity  may  be  generated  by  friction,  but  to 
be  of  practical  service  it  must  flow  continuously  as  a  current. 
Lightning  is  an  electrical  discharge.  Currents  of  electricity 
may  be  generated  by  means  of  voltaic  cells,  and  these  cur- 
rents may  be  conducted  by  wires.  There  are  many  practi- 
cal applications  of  electricity,  as  in  electroplating,  incandes- 
cent lamps,  welding,  flatirons,  electric  bells,  the  electric 
telephone,  and  the  electric  telegraph. 

Michael  Faraday  made  the  greatest  electrical  discovery 
when  he  found  that  a  magnet  if  thrust  quickly  into  a  coil 
of  wire  generates  a  momentary  current  in  one  direction, 
and  if  withdrawn  generates  a  momentary  current  in  the 
opposite  direction..  This  discovery  made  possible  the  in- 
vention of  the  electric  dynamo  and  the  electric  motor. 

Recent  experiments  indicate  that  atoms  of  matter  con- 
tain electricity,  and  that  the  negative  electricity  in  them 
exists  in  the  form  of  exceedingly  minute  particles  called  elec- 
trons. A  current  of  electricity  is  supposed  to  be  a  stream  of 

these  electrons. 

QUESTIONS 

Where  have  you  ever  seen  magnetism  employed  to  man's  ad- 
vantage ? 

What  is  the  relation  between  lightning  and  electricity  ? 

With  what  simple  electrical  devices  are  you  familiar  ? 

In  how  many  different  ways  do  you  know  electricity  to  have 
been  applied  for  your  benefit  ? 

Describe  four  electrical  machines  or  appliances  which  you  con- 
sider of  particular  value. 


CHAPTER   XVII 
WITHIN  THE  EAKTH'S   OEUST 

Beneath  the  Earth's  Surface.  —  Many  excavations  and 
borings  have  been  made  deep  into  the  earth's  crust  and  it 
has  been  found  that  the  temperature  increases  with  the 
depth.  The  rate  of  increase  is  not  the  same  in  different 
places,  nor  is  the  increase  always  uniform  in  the  same 


SAN  MIGUEL  HARBOR  IN  THE  AZORES 
Notice  the  volcanic  cone  in  the  distance. 

place.  The  average  of  a  number  of  deep  excavations  in 
different  parts  of  the  earth  gives  a  rise  of  1°  F.  for  each  70 
or  80  feet  of  descent. 

The  greater  the  pressure  to  which  rocks  are  subjected  the 
more  difficult  it  is  to  melt  them.     If  it  were  not  for  this,  the 
solid  part  of  the  earth  could  not  be  more  than  40  or  50  miles 
502 


BENEATH  THE  EARTH'S  SURFACE  503 

thick,  as  the  interior  heat  would  melt  rocks  under  ordinary 
pressure.  But  the  earth  is  too  rigid  for  its  interior  to  be 
otherwise  than  solid.  So  great  is  the  pressure  to  which  it 
is  subjected  that  probably  none  of  the  material  deep  down 
in  the  interior  of  the  earth  is  in  a  molten  condition. 

If  the  pressure  near  the  surface  should  be  decreased, 
or  if  the  normal  amount  of  heat  at  any  place  should  be 
increased,  the  material  might  become  fused,  and  under 


AN  HAWAIIAN  CRATER 

certain  conditions  might  find  its  way  to  the  surface.  \Ve 
know  that  heated  material  from  below  does  rise  toward  the 
surface  and  intrude  itself  into  the  surface  rocks  and  in 
some  places  pour  forth  over  the  surface. 

What  causes  the  uprising  and  outpouring  of  this  molten 
material  from  below  the  surface  of  the  earth,  and  how  ami 
why  it  reaches  the  surface  are  questions  which  as  yet  are 
unanswerable.  But  as  soon  as  this  igneous  material  comes 
within  the  range  of  observation,  its  properties  and  actions 


504  WITHIN   THE    EARTH'S   CRUST 

can  readily  be  studied.  The  following  descriptions  of  some 
well-known  typical  volcanoes  show  some  of  the  results  of 
subsurface  activity. 

Monte  Nuovo.  —  In  1538,  on  the  shore  of  the  Bay  of 
Naples  near  Baise,  that  once  famous  resort  of  the  Roman 
nobles,  after  a  period  of  severe  earthquake  shocks  there 
suddenly  occurred  a  tremendous  eruption.  From  within 
the  earth  emerged  a  mass  of  molten  material  blown  into 
fragments  by  the  explosion  of  the  included  gases.  Within 
a  few  days  there  was  formed  Monte  Xuovo,  a  hill  440  feet 
high  and  half  a  mile  in  diameter,  having  in  the  top  a  cup- 
shaped  depression  or  crater  over  400  feet  deep. 

So  great  was  the  explosive  force  of  this  eruption  that 
none  of  the  ejected  material  was  poured  out  in  the  form  of  a 
liquid.  The  whole  hill  is  made  up  of  dust,  small  stones,  and 
porous  blocks  of  rock  which  resemble  the  slag  of  a  blast 
furnace.  The  small  fragments  in  such  eruptions  are  called 
ash  or  cinders.  In  a  week  the  eruption  was  over,  and  noth- 
ing of  the  kind  has  since  occurred  in  the  region. 

When  visited  by  the  writer  a  few  years  ago,  the  bottom 
of  the  crater  was  a  level  field  planted  to  corn.  The  whole 
process  of  formation  of  this  volcanic  cone  was  observed  and 
recorded  by  residents  of  the  region.  Other  similar  eruptions 
have  been  observed,  but  perhaps  this  is  the  best  known. 

Vesuvius.  —  WTien  the  Roman  nobles  were  building 
their  magnificent  villas  and  baths  along  the  shore  of  the 
Bay  of  Naples,  the  scenic  beauty  of  the  region  was  greatly 
increased  by  a  mountain  in  the  shape  of  a  truncated  cone, 
which  rose  from  the  plain  a  few  miles  back  from  the  shore. 
Its  sides,  nearly  to  the  summit,  were  covered  with  beautiful 
fields. 


VESUVIUS 


505 


In  the  top  of  the  mountain  was  a  deep  depression  some 
three  miles  in  diameter,  partly  filled  with  water  and  almost 
entirely  surrounded  by  precipitous  rock  cliffs.  There 
were  no  signs  of  internal  disturbance.  Around  the  moun- 
tain were  scattered  prosperous  cities,  the  soil  was  fertile, 
the  vegetation  luxuriant.  To  this  natural  fortress  Spar- 
tacus,  the  gladiator,  retreated  when  he  first  began  to  defy 
the  power  of  Rome. 

In  63  A.D.  the  region  about  the  mountain  was  shaken 
by  a  severe  earthquake  which  did  much  damage.  This 


VESUVIUS  AND  NAPLES 

was  followed  by  other  earthquakes  during  a  period  of  six- 
teen years.  In  August,  79  A.D.,  the  whole  region  was  fright- 
fully shaken,  and  the  previously  quiet  mountain  began  to 
belch  forth  volcanic  dust,  cinders,  and  stones,  so  that  for 
miles  around  the  sun  was  obscured,  and  a  pall  of  utter 
darkness  shrouded  the  country,  lighted  at  intervals  by 
terrific  flashes  of  lightning. 


506  WITHIN   THE    EARTH'S   CRUST 

A  large  part  of  the  ancient  crater,  now  known  as  Monte 
Somraa,  was  blown  away,  and  the  villas  and  towns  near 
the  mountain  were  covered  with  the  ash  and  cinders  ejected. 
So  deep  were  many  of  these  buried  that  their  sites  were 
utterly  forgotten.  Pompeii  and  Herculaneum,  after  lying 
buried  and  almost  forgotten  for  hundreds  of  years,  have 
been  recently  partially  uncovered. 

These  fossil  cities  show  the  people  of  to-day  how  the 
ancient  Romans  lived  and  built.  The  topography  of  the 
country  and  the  coast  line  were'  greatly  changed  by  this  erup- 
tion. Pompeii  formerly  was  a  seacoast  city  at  the  mouth 
of  a  river.  It  is  now  a  mile  or  more  from  the  sea  and  at  a 
considerable  distance  from  the  river. 

From  the  date  of  its  first  historic  eruption  until  the  present 
time  Vesuvius  has  had  active  periods  and  periods  when 
quiet  or  dormant.  Sometimes  the  activity  is  mild,  and  at 
other  times  tremendously  violent.  At  times  the  material 
ejected  is  fragmental  and  at  other  times  streams  of  molten 
lava  pour  down  its  sides.  Its  ever  changing  cone,  unlike 
that  of  Monte  Nuovo,  is  composed  partly  of  ash  and  partly 
of  consolidated  lavas.  Even  as  late  as  1907  a  tremendous 
outpouring  of  ash  took  place  which  devastated  a  con- 
siderable area. 

Mount  Pelee.  —  At  the  north  end  of  the  island  of  Mar- 
tinique in  the  West  Indies  rose  a  conical-shaped  mountain. 
In  a  hollow  bowl-like  depression  at  the  top  lay  a  beautiful 
little  lake  some  450  feet  in  circumference.  The  mountain 
and  lake  were  pleasure  resorts  for  the  people  of  the  city  of 
St.  Pierre.  According  to  legend  this  mountain  had  been 
violently  eruptive,  but  in  historic  time  there  had  been  no 
indication  of  this  except  one  night  in  1851  when  the  volcano 


MOUNT   PELEE 


507 


had  grumbled  and  a  slight  fall  of  volcanic  ash  was  found  in 
the  morning  over  some  of  the  surrounding  region. 

On   April   25,  1902,  people   began  to  see  smoke    rising 
from  the  vicinity  of  the  mountain  and  from  this  time  on 


MOUNT  PELEE  AND  THE  RUINS  OF  ST.  PIERRE 

till  the  final  catastrophe  smoke  and  steam  came  out  in 
small  quantities.  By  May  6  the  volcano  was  in  full  mip- 
tion.  On  the  morning  of  May  6  the  cable  operator  at  St 


508  WITHIN    THE    EARTH'S   CRUST 

Pierre  cabled,  "Red-hot  stones  are  falling  here,  don't 
know  how  long  I  can  hold  out."  This  was  the  last  dis- 
patch sent  over  the  cable. 

About  8  o'clock  on  the  morning  of  the  8th  a  great  cloud 
of  incandescent  ash  and  steam  erupted,  swept  rapidly  down 
the  mountain  toward  St.  Pierre,  and  in  less  than  three 


LAVA  FLOW  IN  THE  HAWAIIAN  ISLANDS 
Liquid  lava  flowing  over  a  cliff. 

minutes  killed  30,000  people,  set  the  city  on  fire,  and  de- 
stroyed 17  ships  at  anchor  in  the  harbor.  Thus  within 
two  weeks  from  the  time  of  the  first  warning  a  rich  and 
densely  populated  region  was  made  a  desolate,  lifeless,  fire- 
swept  desert. 

Distribution  of  Volcanoes.  —  The  number  of  active  vol- 
canoes on  the  earth  is  about  three  hundred.  Most  of  them 
are  situated  on  the  borders  of  the  continents,  on  islands  near 


DISTRIBUTION  OF  VOLCANOES  509 

the  continents,  or  else  they  form  islands  in  the  deep  sea. 
Soundings  show  that  there  are  many  peaks  in  the  sea  which 
have  not  reached  the  surface ;  these  are  probably  volcanic. 
Few  volcanoes  are  far  from  the  sea,  although  there  is  an 


MOUNT  I.AHSKN  IN  ERUPTION 

This  volcano,  after  being  dormant  for  centuries,  suddenly  renewed  its 
activity  in  1914. 

active   crater   in   Africa   several   hundred   miles  from   the 
Indian  Ocean. 

About  800  miles  west  of  Portugal  rises  from  the  depths  of 
the  Atlantic  a  group  of  nine  islands,  the  Azores.    They 


510 


WITHIN   THE    EARTH'S   CRUST 


have  an  area  of  about  1000  square  miles,  and  the  soil  is 
very  fertile.  The  islands  are  mountainous,  one  of  the 
mountains  rising  to  between  7000  and  8000  feet  above  the 
sea.  Then'  formation  is  due  entirely  to  volcanic  forces. 
Islands  of  this  kind  and  coral  islands  are  the  only  projec- 
tions rising  to  the  surface  from  the  deep  ocean  floor. 

In  the  Cordilleran  region  of  the  United  States,  west  of 
the  meridian  of  Denver,  there  are  a  score  or  more  of  lofty 


THE  CITY  OF  ST.  HELENA 

peaks  which  show  conclusive  evidence  of  volcanic  origin. 
Until  the  summer  of  1914  when;^lt.  Lassen  suddenly  began 
to  erupt,  none  of  these  had  been  active  since  white  men 
became  familiar  with  the  region.  In  the  Aleutian  Islands 
are  numerous  volcanoes  which  are  still  active,  and  in  Hawaii 
are  some  of  the  greatest  volcanoes  on  the  earth. 

Extinct  cones  are  sometimes  found  far  in  the  interior  of 
continents,  as  the  Spanish  Peaks  of  Colorado,  which  are 


GEYSERS 


511 


more  than  800  miles  from  the  present  coast.  Many  of 
the  once  active  deep-sea  cones  have  now  become  extinct, 
and  their  gently  sloping  shores  have  been  cut  back  into 
cliffs  which  rise  abruptly  from  the  sea.  One  of  these,  St. 
Helena,  rising  from 
the  depths  of  the 
Atlantic  Ocean,  and 
bounded  by  precipi- 
tous cliffs,  is  noted 
as  being  the  place  of 
exile  of  the  Emperor 
Napoleon  I  of  France. 

Geysers.  —  In  the 
north  island  of  New 
Zealand,  in  Yellow- 
stone National  Park, 
and  in  Iceland,  re- 
markable spouting 
springs  called  geysers 
are  found.  These 
places  have  had  re- 
cent volcanic  ac- 
tivity. The  eruption 
of  a  large  geyser  is 
a  most  picturesque 
and  startling  phe- 
nomenon. Almost 
without  warning  there  is  thrown  into  the  air  a  column 
of  hot  water  from  which  the  steam  escapes  in  rolling  clouds. 
It  rises  in  some  cases  to  a  height  of  a  hundred  feet  or  more 
and  is  maintained  at  nearly  this  height  by  the  ceaseless 


GIANT  GEYSER  IN  ERUPTION 


512 


WITHIN   THE    EARTH'S   CRUST 


outrushing  of  the  water  for  a  time  varying  from  a  few  minutes 
to  between  one  and  two  hours.  Then  it  gradually  quiets 
down  and  dies  away  into  a  bubbling  spring  of  hot  water. 

The  time  at  which  most  geysers  will  erupt  is  uncertain, 
but  there  is  one,  Old  Faithful,  in  Yellowstone  Park,  which 
is  almost  as  regular  as  a  clock,  the  time  between  its  erup- 
tions being  a  little  over  an  hour.  This  geyser  plays  to  the 
height  of  about  150  feet  and  maintains  the  column  of  water 
for  about  four  minutes.  The  Giant  Geyser  of  the  same  re- 
gion throws  a  large  column  of  water  to  a  height  of  250  feet. 
It  plays  from  one  to  two  hours. 

Experiment  161.  —  Fit  a  250  cc.  glass  flask  with  a  two-hole  rubber 
stopper.  Through  one  hole  extend  a  glass  tube  (a)  almost  to  the 
bottom  of  the  flask  and  through  the 
other  hole  a  tube  (b),  5  or  6  cm.  longer 
than  the  height  of  the  flask,  to  within 
about  1  or  2  cm.  of  the  bottom  of 
the  flask.  This  last  tube  should  be 
slightly  drawn  out  at  the  end  and 
bent  at  the  top  so  that  it  slants  away 
from  the  flask.  Arrange  the  flask  on 
a  ring  stand  so  that  it  can  be  heated 
by  a  Bunsen  burner.  Connect  to  the 
tube  (a)  a  rubber  tube  long  enough 

to  reach  into  a  water  reservoir  placed  higher  than  the  top  of  the 
flask  and  to  one  side.  Fill  the  reservoir  with  water.  (Figure  170.) 
Through  the  tube  (6)  "  suck  "  the  air  out  of  the  flask  until  the 
water  from  the  reservoir  begins  to  run  into  the  flask.  A  siphon  will 
be  formed  which,  when  there  is  no  internal  pressure,  will  keep  the 
water  in  the  flask  slightly  above  the  bottom  of  the  tube  (fc) .  Now 
heat  the  flask.  When  steam  begins  to  form,  hot  water  will  be 
thrown  out  of  the  tube  (6)  until  its  lower  end  becomes  uncovered 
and  the  pressure  of  the  steam  relieved.  Water  from  the  reservoir 
will  then  run  in  again,  slightly  covering  the  end  of  the  tube.  As 
soon  as  more  steam  is  formed,  hot  water  will  be  ejected  as  before. 


FIGURE  170 


EARTHQUAKES 


513 


Thus  a  spray  of  hot  water  is  intermittently  ejected  from  the  flask 
as  long  as  heating  continues.  We  have  here  an  action  which  re- 
sembles that  of  a  geyser. 

The  outpouring  hot  water  brings  lip  with  it  dissolved 
rock  and  as  the  spray  falls  back  and  cools,  this  is  deposited, 
forming  craters  of  singular  shape  and  grotesque  beauty. 
On  looking  into  these  craters  a  smoothly  lined,  irregular, 

crooked,    tubelike  open- 

ing  is  seen  to  extend 
down  into  the  ground. 
It  is  through  this  that 
the  water  finds  its  way 
to  the  surface.  How  long 
these  tubes  are  nobody 
knows,  but  they  must 
reach  to  a  point  where 
the  heat  is  sufficient  to 
raise  water  to  its  boiling 
point.  This  heat  is  prob- 
ably due  to  hot  sheets  of 
lava. 

When  the  water  in  the 
tube  is  heated  enough  to 
make  it  boil  under  the  pressure  to  which  it  is  subjected, 
steam  forms  and  some  of  the  water  is  pushed  out  over  the 
surface.  This  escape  of  water  relieves  some  of  the  pressure, 
and  more  of  the  water  far  down  in  the  tube  expands  into 
steam,  thus  throwing  more  water  out.  Huge  indeed  must 
be  the  reservoir  to  which  the  tube  in  a  geyser  like  the  Giant 
leads,  to  be  able  to  pour  out  such  a  vast  quantity  of  water. 

Earthquakes.  —  In  mountain  regions  which  are  young 
or  still  growing,  earthquakes  are  not  uncommon.  These 


FAULT  LINE  OF  AN  EARTHQUAKE 


514 


WITHIN   THE   EARTH'S   CRUST 


are  due  to  breaks  or  slips  of  a  few  inches  or  a  few  feet  in  the 
rock  structure.  From  the  place  at  which  the  break  or  slip 
takes  place  the  motion  is  transmitted  through  the  rock  mass 
to  the  surface,  where  it  causes  sudden  and  often  tremendous 
shocks.  These  slippings  may  occur  occasionally  for  ages 

along  the  same  fault  line. 
Sometimes  they  are  in- 
tense enough  to  cause 
great  damage;  at  other 
times  only  a  slight  tremor 
is  felt. 

The  rapidity  of  the 
transmission  of  the  shock 
differs  with  the  kind  of 
material  through  which 
it  is  transmitted,  varying 
from  a  few  hundred  feet 
to  several  thousand  feet 
per  second.  The  nearer 
a  place  is  to  the  break 
or  slip  the  greater  is  the 
intensity  of  the  shock. 
Sometimes  the  crack  or 
fault  along  which  the  movement  occurs  reaches  to  the 
surface  and  makes  the  displacement  apparent. 

If  an  earthquake  originates  under  the  sea,  a  great  wave  may 
be  developed  which  rushes  inland  from  the  coast,  causing 
great  destruction.  One  of  the  most  fearful  of  these  waves 
occurred  at  Lisbon,  Portugal,  in  1755,  sweeping  away  thou- 
sands of  people  who  had  rushed  into  an  open  part  of  the  city 
to  get  away  from  the  falling  buildings  caused  by  the  earth- 
quake shock. 


FENCE  BROKEN  BY  THE  SLIPPING  OF  THE 
EARTH  ALONG  A  FAULT  LINE 


MINING  IN  MOUNTAIN  REGIONS 


515 


Sometimes  earthquakes  are  followed  by  terrible  fires 
which  cannot  be  extinguished  on  account  of  the  disarrange- 
ment of  the  water  supply.  This  was  the  case  in  the  San 
Francisco  earthquake.  With  the  care  taken  in  rebuilding 


SAN  FRANCISCO  FIRE 

The  direct  damage  to  property  and  loss  of  life  by  earthquake  in  1906  was 
insignificant.  The  disarrangement  of  the  water  supply  made  possible 
one  of  the  greatest  conflagrations  in  history.  Extraordinary  precautions 
were  taken  in  relaying  the  water  mains  of  the  risen  city. 

that  city  and  in  laying  its  water-mains,  it  is  unlikely  that 
any  such  disaster  could  ever  follow  another  earthquake  of 
the  same  sort. 

Mining  in  Mountain  Regions.  —  When  rocks  are  folded 
and  crushed,  in  forming  mountains,  heat  is  generated,  and 
heated  water  under  pressure  acts  upon  the  components  of 
the  rocks  and  dissolves  some  of  their  minerals,  which  ac- 
cumulate in  cracks  and  crevices  called  veins.  When  the  over- 
lying beds  have  been  worn  away,  these  mineral  veins,  formed 


516 


WITHIN   THE    EARTH'S   CRUST 


deep  below  the  surface,  are  exposed  and  can  be  mined. 
Mountains  are  therefore  the  great  regions  for  the  mining  of 
metals. 

In  this  country  mining  is  a  most  important  industry  in 
the  Sierra  Nevada  Mountains  and  in  the  Appalachian  re- 
gion. In  one  are  found  great  quantities  of  copper,  silver, 


PLACER  MINING  IN  THE  SIERRAS 
The  sand  is  washed  from  the  gold  by  huge  streams  of  water. 

and  gold,  and  in  the  other  iron  and  coal.  In  the  old  Lauren- 
tian  Mountain  region,  near  the  Great  Lakes,  much  copper 
is  found.  The  Alps  and  the  Pyrenees  are  among  those 
mountains  that  have  few  minerals. 

The  Story  of  Coal.  —  We  have  learned  that  warm,  moist 
air  is  necessary  for  the  activities  of  the  bacteria  of  decay. 
Where  there  is  too  much  water  and  not  enough  air  the  con- 
ditions are  not  favorable  for  complete  decay.  Wlien  plants 


THE  STORY  OF  COAL 


517 


die  and  fall  into  water,  they  undergo  changes  but  not  the 
changes  that  occur  in  air.  Most  of  the  carbon,  which  in 
the  air  would  be  oxidized  into  carbon  dioxide,  is  preserved 
under  water. 

Where  vegetation  grows,  dies,  and  falls  into  water  year 
after  year  for  great  lengths  of  time,  the  plant  remains  will 


DIOOINQ  PEAT  IN  IRELAND 

gradually  accumulate  until  they  fill  the  swamps  in  which 
they  have  grown  or  the  lakes  which  they  have  bordered. 
This  explains  the  formation  of  great  peatbogs  in  Ireland 
and  in  other  parts  of  the  world.  Some  of  the  peatbogs 
of  Ireland  are  more  than  forty  feet  deep,  and  the  spongy 
peat  when  cut  and  dried  furnishes  the  most  widely  used 


518 


WITHIN   THE    EARTH'S   CRUST 


fuel  of  that  country.  That  such  bogs  are  filled  lakes  or 
swamps  and  that  it  has  taken  thousands  of  years  for  the 
peat  to  accumulate,  is  shown  by  the  fact  that  hollowed 


Courtesy  of  Taylor  Coal  Co. 
COAL  MINING  IN  SOUTHERN  ILLINOIS 

Using  a  pneumatic  drill,  preparatory  to  blasting.     Notice  the  horizontal 
layers  in  which  the  coal  lies. 

logs  used  as  canoes  by  prehistoric  men  are  sometimes  found 
buried  in  the  peat  at  a  depth  of  thirty  feet  or  more. 

If  these  peat  accumulations  should  at  some  time  be  grad- 
ually submerged  and  covered  with  sand  and  silt,  the  ever- 
increasing  pressure  of  the  water  and  of  the  layers  of  sediment 
would  gradually  compress  the  spongy  mass  of  vegetation 


THE   STORY  OF  COAL  519 

into  compact  layers.  In  the  course  of  ages  these  layers 
would  harden  and  change  into  seams  of  bituminous  (soft) 
coal.  The  overlying  layers  of  sand  and  mud  would  change 
into  layers  of  sedimentary  rock. 

This  process  has  been  repeated  many  times  in  the  history 
of  the  earth.  In  fact  there  are  some  sections  where  it  has 
happened  more  than  once  over  the  same  area,  and  has  re- 
sulted in  the  formation  of  several  seams  of  coal,  one  above 
the  other,  with  layers  of  sedimentary  rock  between.  If  in 
after  ages  such  seams  of  coal  were  heated  by  the  folding  of 
the  earth's  crust,  or  by  some  other  means,  the  bituminous 
coal  was  changed  into  anthracite  (hard)  coal. 

Sometimes  miners  find  the  roots  of  ancient  trees,  now 
changed  into  coal,  projecting  from  the  bottom  of  a  seam  of 
coal  into  the  underlying  rock  layers  that  formed  the  soil 
in  which  this  ancient  vegetation  grew.  Sometimes  the 
impressions  of  leaves  and  plant  stems  are  found  in  the 
underlying  or  the  overlying  rock  layers  and  even  in  the  coal 
itself. 

How  dependent  the  greater  part  of  the  civilized  world 
is  upon  nature's  supply  of  coal,  for  comfort  and  for  com- 
merce, was  shown  during  the  coal  famine  of  the  winter  of 
1917-1918  in  our  Eastern  and  Middle  states.  Coal  is  a 
plentiful  commodity  in  normal  times,  and  in  many  sections 
is  very  cheap;  but  considering  that  nature  has  required 
ages  to  form  and  preserve  it,  and  that  what  now  seems  an 
unlimited  supply  must  some  day  be  exhausted,  the  prodigal 
waste  of  coal  of  which  recent  generations  have  been  guilty 
is  a  serious  matter. 

Petroleum  is  probably  the  result  of  the  decomposition  of 
animal  and  plant  remains  which  have  been  subjected  for 
ages  to  heat  and  enormous  pressure.  By  distilling  petroleum, 


520  WITHIN   THE   EARTH'S   CRUST 

or  crude  oil  as  it  is  generally  called,  many  different  products 
are  obtained,  among  which  are  gasoline,  kerosene,  benzine, 
paraffin,  and  various  lubricating  oils. 

The  crude  oil  itself  is  burned  in  many  sections  to  produce 
heat  and  power.     For  many  purposes  it  is  better  than  coal, 


OIL  WELLS 
Tapping  the  rock  layers  containing  petroleum. 

since  the  same  amount  of  fuel  can  be  carried  in  less  space. 
The  supply  of  oil  seems  to  be  even  more  limited  than  that 
of  coal,  but  it  has  been  wasted  at  times  fully  as  recklessly. 
In  the  interest  of  future  generations,  both  coal  and  oil 
should  be  more  carefully  conserved. 

SUMMARY 

Many  excavations  and  borings  into  the  earth's  crust  have 
shown  that  temperature  increases  with  depth.  If  it  were 
not  for  the  tremendous  pressure  of  outside  layers  of  matter, 
the  heat  at  the  interior  of  the  earth  would  probably  cause 
the  matter  there  to  be  in  a  molten  condition.  If  from 


QUESTIONS  521 

solid  matter  heated  to  such  a  temperature,  pressure  should 
be  withdrawn,  or  if  the  normal  heat  should  be  increased, 
the  heated  matter  might  become  molten  and  find .  its  way 
to  the  surface.  What  causes  uprising  and  outpouring  of 
molten  material  is  a  question  that  is  at  present  unanswer- 
able. We  know  only  that  this  does  occur,  and  has  resulted 
in  such  volcanoes  as  Monte  Nuovo,  Mount  Pelee,  Vesuvius, 
and  other  less  famous  volcanoes  all  over  the  world.  Geysers 
are  spouting  hot  springs  that  are  found  in  regions  of  recent 
volcanic  activity.  Earthquakes  are  shocks  communicated 
to  the  surface  of  the  earth  from  breaks  or  slips  in  rock 
structure  of  the  earth's  crust. 

Mountains  are  the  great  regions  for  the  mining  of  metals. 
It  is  supposed  that  the  heat  generated  by  the  folding  and 
crushing  of  the  earth's  crust  in  these  regions  has  brought 
about  the  accumulation  of  the  metal  in  cracks  or  crevices 
called  veins.  Bituminous  coal  is  a  sedimentary  rock  of 
vegetable  origin,  which  has  been  deposited  under  such 
conditions  that  the  carbon  instead  of  being  oxidized  was 
preserved. 

QUESTIONS 

What  is  the  probable  condition  of  the  earth's  interior? 

Describe  the  eruption  and  present  condition  of  Monte  Nouvo. 

What  has  been  the  history  of  Vesuvius? 

What  is  Mount  Pelee's  story? 

Describe  a  geyser. 

What  causes  earthquakes? 

How  has  coal  been  formed? 


CHAPTER  XVIII 
LIFE  AS  BELATED  TO  PHYSICAL  CONDITIONS 

Ancient  Life  History.  —  As  the  rock  layers  of  the  earth 
are  explored,  fossils  of  different  kinds  of  plants  and  animals 
are  discovered.  The  fossils  of  the  more  recent  rock  layers 


PETRIFIED  TREES 
Found  near  Holbrook,  Arizona. 

correspond  very  closely  to  the  plants  and  animals  that  are 
found  upon  the  earth  to-day,  but  the  older  the  layers,  the 
less  they  correspond.  There  seems  to  have  been  a  gradual 
development  in  life  forms  through  the  past  ages,  a  frag- 
522 


ANCIENT  LIFE  HISTORY  523 

mentary  record  of  which  is  engraved  upon  certain  of  the 
sedimentary  rocks.  Rocks  which  were  formed  under  dif- 
ferent conditions  contain  different  species  of  life-forms, 
showing  that  throughout  all  time  the  geographic  condition 
has  had  a  marked  influence  upon  plants  and  animals. 

The  rocks  and  fossils  also  show  that  the  geographical 
conditions   of   certain   areas   have   varied  greatly.     Some 


SKELETON  OF  AN-  ANCIENT  AMERICAN  ELEPHANT 
Found  near  Los  Angeles,  California. 

regions  have  been  below  and  above  the  sea  several  times. 
Regions  now  cold  have  been  warm,  and  those  now  dry  have 
been  wet,  and  vice  versa.  Thus  the  life  in  certain  areas  has 
suffered  great  changes  by  the  geographical  accidents  to 
which  the  region  has  been  subjected.  The  petrified  forests 
near  Holbrook,  Arizona,  show  some  of  the  most  remarkaMr 
tree  fossils  ever  found  and  indicate  that  the  region  has  been 
subjected  to  remarkable  geographical  changes. 


524      LIFE  AS   RELATED   TO   PHYSICAL  CONDITIONS 


Distribution  of  Life.  —  Plants  and  animals  are  found 
wherever  the  conditions  are  suitable  for  their  existence. 
The  surface  of  the  earth  is  a  universal  battlefield  of  plants  and 

animals  struggling  to 
exist  and  to  in- 
crease. They  extend 
themselves  wherever 
attainable  space  is 
opened.  But  barriers 
may  oppose  their 
spread  and  geo- 
graphical accidents 
may  drive  them  from 
areas  which  they  had 
heretofore  held.-  The 
retreat  of  the  sea  may 
cause  a  change  in  the 
position  of  shore  life. 
In  the  water  a  land 
barrier  or  an  expanse 
of  deep  water  may 
prevent  the  spread 
of  shore  forms.  On 
the  land  a  mountain 
uplift,  a  desert  area, 

or  a  water  barrier  may  limit  the  space  occupied  by  animal 
and  vegetable  species. 

Certain  plants  and  animals  are  much  more  widely  dis- 
tributed than  others.  Plants  like  the  dandelion  and  thistle, 
whose  seeds  are  easily  blown  about  by  the  wind,  spread 
rapidly,  while  trees  like  the  oak  and  chestnut  spread  slowly. 
As  plants  have  not  the  power  to  move  about,  they  cannot 


GILA  MONSTERS 

These  are  very  poisonous  reptiles  of  the 
southwestern  American  desert. 


EFFECT   OF   THE   GLACIAL  PERIOD 


525 


distribute  themselves  as  easily  as  animals.  Certain  birds 
which  are  strong  of  flight  are  found  widely  distributed  over 
regions  separated  by  barriers  impassable  to  other  animals. 

Some  of  the  present  barriers  to  life  distribution  have  come 
into  existence  in  comparatively  recent  geological  time. 
There  is  good  reason  to  believe  that  the  British  Isles  and 
Europe  were  formerly  connected,  and  that  in  very  ancient 
times  Australia  was  joined  to 
Asia.  It  is  also  believed  that 
for  long  ages  North  and  South 
America  were  separated  by  a 
water  barrier  and  that  even  after 
they  were  once  connected,  the 
Isthmus  of  Panama  was  again 
submerged. 

These  are  but  a  few  illustra- 
tions of  the  changes  in  the  earth's 
surface  which  have  affected  the 
distribution  of  animals  and 
plants.  Climatic  changes  like 
that  which  brought  about  the 
great  ice  advance  of  the  Glacial 
Period  have  affected  in  a  marked 
degree  the  distribution  of  life. 
It  is  thus  found  that  when  a  study  is  made  of  the  present 
distribution  of  life,  careful  attention  must  be  given  to  the 
present  and  past  geographical  conditions  of  the  region. 

Effect  of  the  Glacial  Period  upon  Plants  and  Animals.  — 
All  plants  and  animals  were  forced  either  to  migrate  be- 
fore the  slowly  advancing  ice  or  to  suffer  extermination. 
Individual  plants,  of  course,  could  not  move,  but  as  the  ice 


CANADA  THISTLE 

One  of  the  most  widely  dis- 
tributed of  plants. 


526      LIFE   AS   RELATED  TO  PHYSICAL  CONDITIONS 

spread  toward  the  south  with  extreme  slowness  and  with 
many  halts,  the  plants  of  colder  latitudes  found  conditions 
suitable 'for  their  growth  ever  opening  toward  the  south. 
They  were  thus  induced  to  spread  in  that  direction,  so 
that  at  the  time  of  the  greatest  extension  of  the  ice  the 
plants  suitable  to  a  cold  climate  had  penetrated  far  to  the 
south  of  their  former  habitat. 

As  the  ice  receded,  these  cold-loving  plants  were  forced 
to  follow  its  retreat  or  to  climb  the  mountains  in  order  to 
obtain  the  climate  they  needed.  They  did  both,  so  that 
in  areas  once  covered  by  the  ice,  plants  similar  to  those  of 
far  northern  regions  are  found  on  the  tops  of  the  mountains 
in  middle  latitudes.  What  was  true  of  the  plants  was  true 
also  of  the  animals. 

Waterfalls  Due  to  Glaciation.  —  As  the  ice  spread  over  the 
country  it  filled  the  river  valleys  in  many  places  with  debris. 
When  the  ice  melted  away,  some  rivers  could  no  longer 
find  their  old  courses  and  were  forced  to  seek  new  ones. 
In  its  new  course  a  stream  might  fall  over  a  cliff. 

The  Merrimac  furnishes  a  fine  example  of  water  power 
due  to  glaciation.  The  great  manufacturing  cities  of  Lowell, 
Lawrence,  and  Haverhill  would  not  exist  had  not  the  river 
been  displaced  from  its  previous  channel  by  the  glacial  ice, 
and  in  developing  its  new  valley  come  upon  ledges.  The 
Niagara  is  another  notable  example  of  vast  water  power 
due  to  the  displacement  of  drainage  by  the  ice.  It  is  probable 
that  in  pre-glacial  time  there  was  a  river  which  carried  off 
the  drainage  of  the  area  now  drained  by  the  Niagara,  but 
it  did  not  flow  where  the  Niagara  now  flows. 

Thus  we  see  that  the  hum  of  the  spindle  and  the  lathe 
are  often  but  the  modulated  whispers  of  those  ancient  forces 


WATERFALLS  DUE  TO  GLACIATION  527 


YOSEMITE  FALLS 
A  wonderfully  beautiful  waterfall  due  to  glacial  action. 


528      LIFE   AS   RELATED   TO   PHYSICAL  CONDITIONS 


which  thousands  of  years  ago  sorted  the  rock  materials  and 
built  the  vast  continental  ice  palaces  of  the  Glacial  Period. 

Adaptability  of  Life.  —  There  is  hardly  a  place  on  the 
earth's  surface  not  adapted  to  some  form  of  life.  Even  upon 
the  ice-bound  interior  of  Greenland  a  microscopical  plant 

and  a  tiny  worm 
have  found  a  home. 
The  dry  desert  re- 
gions have  a  few 
plants  with  small 
leaves  or,  like  the 
cactus,  with  no  true 
leaves.  Lack  of 
leaves  prevents  the 
evaporation  of  the 
water  from  plants 
and  so  protects  them 
from  drought. 

Another  example 
of  adaptability  is  the 
fact  that  the  small 
animals  of  the  desert 
are  generally  of  a 
sandy  color,  which 
makes  them  hardly 
distinguishable  from 
their  desert  sur- 
roundings. The  large 
CACTI  ones  are  swift,  strong 

These    are    adapted    to    desert    life    because       runnerS)  like  the  an- 
they  have  no  leaves  from  which  water  can 
evaporate.  telope     and     ostrich, 


ADAPTABILITY  OF  LIFE 


529 


RATTLESNAKE  COILED  READY  TO  rfphi.Nc; 

The  color  of  these  reptiles  makes  them 
hardly  distinguishable  from  the  sur- 
rounding desert. 


or,  like  the  camel,  are 
able  to  travel  for  long 
distances  without  water. 
In  the  colder  regions 
the  plants  have  the  power 
of  rapid  growth  and 
germination  during  the 
short  season  when  the 
snow  has  melted  away. 
Then,  during  the  long 
winter,  they  lie  dormant  but  unharmed  under  the  snow  and 
ice.  The  animals  are  either  able,  like  the  reindeer,  to  live 
upon  the  dry  mosses,  lichen,  and  stunted  bushes,  or  else 

upon  other  animals. 
Their  color,  like  that 
of  the  polar  bear, 
often  blends  with 
their  surroundings. 

Some  animals  have 
a  wide  range  of 
adaptability,  like  the 
tiger,  which  is  found 
from  the  equator  to 
Siberia.  But  usually 
the  range  of  an  ani- 
mal species  is  much 
more  restricted,  since 
it  is  seldom  able  to 
adapt  itself  to  widely 
differing  conditions.  The  surrounding  region,  the  eleva- 
tion, the  temperature,  the  amount  of  moisture,  the  soil, 
the  kinds  of  winds  and  their  force,  all  have  a  marked 


A  HERD  OF  REINDEER 

This  animal  is  of  invaluable  service  to  man 
in  polar  regions. 


530      LIFE   AS   RELATED   TO   PHYSICAL  CONDITIONS 

effect   upon   the  fauna   (animals)    and  flora  (plants)   of   a 
country. 

The  species  that  thrive  in  a  region  must  have  adapted 
themselves  to  the  existing  conditions,  yet  other  animals 
and  plants  may  be  as  well  adapted  for  certain  regions  as 
those  now  inhabiting  them.  Striking  examples  of  this 


CALIFORNIA  RABBIT  DRIVE 

In  some  localities  rabbits  become  such  a  pest  that  the  inhabitants  turn 
out  in  a  body,  drive  them  into  inclosures,  and  kill  them. 

are  the  English  sparrow  and  the  gypsy  moth,  which  have 
spread  with  such  tremendous  rapidity  since  their  introduc- 
tion into  this  country.  The  rabbit  in  Australia  and  southern 
California  is  another  striking  example.  The  adaptability 
of  plants  to  a  new  region  is  also  illustrated  by  the  Russian 
thistle  which  was  introduced  into  this  country  in  1873  and 
which  has  now  become  a  national  pest. 


LIFE  OF  THE  SEA  531 

Life  of  the  Sea.  —  The  plants  living  in  the  sea  are  nearly 
all  of  a  low  order.  The  mangrove  trees  which  border  some 
tropical  shores  represent  their  highest  type.  The  most 
abundant  of  sea  plants,  the  seaweeds,  have  no  flower  or 


DIFFERENT  KINDS  OF  SEAWEED 


seed  or  true  root,  although  most  of  them  have  an  anchoring 
device  by  which  they  are  attached  to  the  bottom, 
food  is  absorbed  from  the  surrounding  water.    They  have 
developed  little  supporting  tissue,  but  instead  have  bladder- 
like  air  cavities  or  floats,  which  enable  them  to  maintain 


532      LIFE   AS   RELATED   TO   PHYSICAL   CONDITIONS 


an  upright  position  or  to  float  freely  in  the  water.     Usually 
they  abound  near  the  shore  where  the  water  is  shallow. 

The  vast  surface  of  the  open  sea  supports  few  plants 
except  the  minute  one-celled  plants,  the  diatoms,  of  which 
there  are  many  species  and  an  almost  infinite  number  of 
individuals.  These  furnish  about  the  only  food  for  the 
animals  of  the  open  sea  except  that  obtained  by  preying 
upon  one  another. 

A  great  quantity  of  detached  seaweed  (Sargassuni) ,  filled 
with  multitudes  of  small  marine  animals  and  the  fishes 

which  prey  upon 
them,  covers  the  sur- 
face of  the  middle 
Atlantic,  the  center 
of  the  oceanic  eddy. 
Through  this  Colum- 
bus sailed  from  the 
16th  of  September 
to  the  8th  of  Octo- 
ber, 1492,  greatly  to 
his  own  astonishment 
and  to  the  terror  of 
his  crew,  who  had  never  before  heard  of  these  "  oceanic 
meadows." 

The  animals  of  the  sea  vary  in  size  from  the  microscopic 
globigerina  (page  400),  whose  tiny  shells  blanket  the  beds 
of  the  deeper  seas,  to  the  whale,  that  huge  giant  of  the  deep, 
in  comparison  with  which  the  largest  land  animals  are  but 
pygmies.  Although  monarch  of  all  the  finny  tribe,  it  is 
not  a  fish  at  all,  but  a  mammal  which  became  infatuated 
with  a  salt-water  life  and  so  through  countless  ages  has  more 
and  more  assumed  the  finny  aspect.  It  is  obliged  to  rise 


A  SMALL  SHARK 
Photographed  under  water. 


LIFE   OF  THE   SEA  533 

to  the  surface  to  breathe.     It  cares  for  its  young  like  other 
mammals. 

Here,  too,  are  found  the  jellyfish,  the  Portuguese  man-of- 
war  (Figure  171),  some  fishes,  many  crustaceans,  a  few  in- 
sects, turtles,  snakes,  and  mammals.  Most  of  these  animals 
are  lightly  built  and  are  well  equipped  for  floating  and 
swimming.  Some  sea  animals,  like  the  oyster,  barnacle, 
and  coral  polyp,  are  fixed,  and  rely  upon  the  currents  of 
the  water  to  bring  them  their  food,  while  others,  like  the 
crab,  the  lobster,  and  the  fish,  move  from  place 
to  pi  ice  in  search  of  prey. 

In  the  warmer  seas  the  surface  water  is  often 
filled  with  minute  microscopical  animals  which 
have  the  power,  when  disturbed,  of  emitting 
light,  so  that  when  a  boat  glides  through  these 
waters  at  night,  a  trail  of  sparkling  silver,  called 
phosphorescence,  seems  to  follow  in  the  wake. 

Between  the  surface  and  the  bottom  of  the  FlGURE  1T1 
deep  ocean  there  seems  to  be  a  vast  depth  of  water  alni<»t 
devoid  of  life.  This  region,  like  the  bottom  of  the  ocean, 
has  been  little  explored  and  there  may  be  life  here  which  has 
not  been  discovered.  From  the  bottom  of  the  sea  the 
dredge  has  brought  up  some  very  curious  forms  of  life. 
Here  under  tremendous  pressure  and  in  profound  darkness 
have  been  developed  species  of  carnivorous  fishes. 

Some  of  these  have  large,  peculiarly  well-developed  eyes 
and  others  have  not  even  the  rudiments  of  eyes.  As  the 
light  of  the  sun  never  penetrates  to  these  depths,  it  would 
seem  at  first  that  eyes  could  be  of  no  use,  but  it  has  brni 
found  that  some  of  the  animals  of  the  ocean  bottom  have 
the  power  of  emitting  light  in  some  such  way  as  the  glow- 
worm and  firefly  do,  and  it  is  probable  that  it  is  to  see 


534      LIFE  AS   RELATED   TO   PHYSICAL  CONDITIONS 


FLYING  FISH 

Notice  how  the  front  fins  have  become 
wing-like 


this  phosphorescent  light  that  the  eyes  of  the  animals  are 
used.     There  are  no  plants  here  and  the  life  is  much  less 

abundant  and  less 
varied  than  near  the 
surface. 

There  is  but  little 
variation  in  the  con- 
ditions surrounding 
the  animals  of  the 
sea,  and  so  the  organs 
corresponding  to 
these  conditions  are 
not  diverse.  Living 
in  a  buoyant  medium 
dense  enough  to  sup- 
port their  bodies,  and  of  almost  unvarying  temperature,  the 
sea  animals  have  never  required  or  developed  varied  organs 
for  locomotion,  like 
the  wing,  the  hoof 
and  the  paw,  or  for 
protection  from  cold, 
like  the  feather,  the 
hair,  or  wool.  It  is 
true  that  certain  sea 
dwellers,  like  the  seal, 
are  covered  with 
hair,  but  these  air 
breathers  were  prob- 
ably originally  a  land 
type  and  have  ac- 
quired the  habit  of  SEALS 

living    in    the    water.  Originally  land  animals. 


LIFE   OF  THE   LAND 


535 


The  highest  traits  of  animal  life,  such  as  are  found  in  land 
animals,  have  not  been  required  or  acquired  by  the  sea 
animals,  and  although  the  number  of  species  and  kinds 
is  very  great,  there  is  not  found  among  them  the  same  grade 
of  intelligence  or  power  of  adaptability,  as  among  the 
land  animals. 


Life  of  the  Land.  —  The  highest  development  of  both 
plant  and  animal  life  is  found  upon  the  land.  Here  at  the 
meeting  place  of  the  solid 
earth  and  its  gaseous  en- 
velope, subjected  to  great 
variations  in  amount  of 
sunlight,  moisture,  tem- 
perature, and  soil,  the 
plants  and  animals  have 
acquired  a  marvelous 
variety  of  forms  and 
structures  to  adapt  them 
to  their  varied  surround- 
ings, and  to  enable  them 
to  secure  a  living. 

Some  plants  lift  their 
strong  arms  high  into  the 
air  to  intercept  the  sun- 
beams before  they  strike 
the  earth,  while  others 
clothe  the  surface  with  a  dress  of  varied  green. 


,  „          PMCKLY  PHLOX 

Notice  the  thorns  by  which  it  protects 
itself. 


In  some 


plants,  odor,  nectar,  or  juicy  berries  attract  the  animals 
whose  aid  is  needed  for  fertilizing  and  scattering  their  weds, 
while  in  others,  noxious  odors,  prickles,  thorns,  and  acrid 
secretions  ward  away  animals  destructive  to  their  welfare. 


536      LIFE  AS   RELATED   TO   PHYSICAL  CONDITIONS 


The  highest  perfection  of  beauty,  utility,  and  productiveness 
among  plants  has  been  reached  by  those  of  the  land. 

The  animals  of  the  land,  surrounded  by  the  air,  which 
bears  no  food  solutions  to  inert  mouths,  must  be  well  en- 
dowed with  the  power  of  motion  in  order  to  procure  their 
food.  They  must  either  crawl 
over  the  surface  or  be  provided 
with  appendages  to  support  their 
weight  against  gravity.  There  is 
no  floating  indolently  in  the  air  as 
in  the  water.  Movement,  exer- 
tion, search,  are  the  requisites  of 
life  on  land.  The  eggs  and  young, 
as  a  rule,  cannot  be  abandoned  to 
hatch  and  to  care  for  themselves ; 
the  nest,  the  burrow,  the  den  must 
be  provided.  This  is  the  realm  of 
homes. 

The  land  animals  are  also  the 
most  intelligent.  Birds  long  ago 
solved  the  problem  of  flight  for  a 
body  heavier  than  air,  which  is 
now  being  successfully  solved  by 
man  after  years  of  effort.  Cer- 
tain animals,  like  the  bee,  the 
ant,  and  the  squirrel,  have  the  provident  habit  of  storing 
up  food  in  the  summer  against  a  day  of  need.  Other  ani- 
mals, like  the  birds,  have  learned  to  migrate  to  a  warmer 
clime  when  winter  comes.  The  beaver  is  probably  the 
pioneer  in  hydraulic  engineering.  When  he  feels  the  need 
of  a  water  reservoir,  he  builds  a  dam  and  makes  it.  To- 
day many  a  swamp  in  the  northern  states  owes  its  origin 


BIRD'S  NEST 
A  simple  home. 


DISTRIBUTION  OF  ANIMALS 


537 


to  him.  Wonderful  indeed  is  the  intelligence  of  many  of 
the  land  animals,  due  in  large  part  to  their  development 
amid  varied  geographical  conditions. 


DOUBLE  BEAVER  DAM  AND  BEAVER  HOUSE 

In  the  foreground,  one  of  the  dams  is  plainly  visible.  In  the  background 
is  a  second  dam  running  almost  parallel  to  the  first.  To  the  right  in 
the  quiet  water  is  the  beaver  house.  To  the  left  are  stumps  of  trees 
that  were  felled  by  the  beavers.  Picture  taken  in  Estes  Park,  Colorado, 
by  Frank  M.  Hallenbeck  of  Chicago. 

Distribution  of  Animals.  —  An  examination  of  a  globe 
shows  (1)  that  the  land  is  massed  around  the  north  pole, 
(2)  that  the  three  continental  masses  to  the  south  are 
separated  from  one  another  by  wide  seas,  and  (3)  that 
while  two  of  these  are  connected  by  narrow  strips  of  land 
to  northern  continents,  the  third  is  entirely  separated  from 
all  other  land. 

But  slight  changes  in  elevation  would  connect  the  northern 
continents  with  one  another.  As  they  are  so  closely  related 


538      LIFE  AS   RELATED   TO  PHYSICAL   CONDITIONS 


to  one  another,  it  might  be  expected  that  the  animals  of 
these  continents  would  resemble  one  another,  particularly 

in  the  more  northern 
parts.  This  is  true. 
Bears,  wolves,  foxes, 
elk,  deer,  and  sheep  of 
nearly  related  species 
are  found  distributed 
over  the  northern  con- 
tinents. 

The  animals  of  the 
southern  continents 
are  much  less  nearly 
related.  The  ostrich, 
giraffe,  zebra,  and  hip- 
popotamus are  among 
the  characteristic  ani- 
mals of  Africa  which  are  not  found  elsewhere.  In  South 
America  the  tapir,  great  anteater,  armadillo,  and  llama 
are  among  the  animals  not  represented  elsewhere.  Both 
of  these  continents, 
however,  have  ani- 
mals closely  related 
to  those  of  other 
great  divisions,  show- 
ing that  their  present 
isolation  has  not  con- 
tinued far  back  in 
geological  time. 

The     animals     of 
Australia     differ 

Many  opossums  have  no  pouch  but  carry 
greatly     from      those  their  young  on  their  backs. 


OSTRICHES 
The  largest  of  all  birds. 


OPOSSUM 


DISTRIBUTION  OF  ANIMALS  539 

of  the  other  continents.  The  quadrupeds  here  are  marsu- 
piah,  animals  which  usually  carry  their  young  in  a  pouch. 
The  only  members  of  the  family  existing  at  present  else- 
where are  the  American  opossums.  The  largest  of  the 
marsupials  is  the  great  kangaroo,  which  measures  between 
seven  and  eight  feet  from  its  nose  to  the  tip  of  its  tail.  Al- 
though it  has  four  feet,  yet  it  runs  by  making  extraordinary 


KANGAROO  FEEDING 

leaps  with  its  strong  hind  feet.  Here  is  also  found  one  of 
the  most  singular  of  all  living  animals,  the  duckbill,  the 
lowest  of  all  quadrupeds,  which  in  its  characteristics  re- 
sembles both  quadrupeds  and  birds. 

All  this  seems  to  show  that  the  distribution  and  devel- 
opment of  the  animals  of  the  different  continents  have  been 
largely  dependent  upon  the  former  geographical  relations 
of  the  land  masses.  The  native  animals  of  a  region  are 


540      LIFE   AS   RELATED   TO   PHYSICAL  CONDITIONS 


not  necessarily  the,  only  ones  suited  to  it ;  animals  from 
other  places  may  be  even  better  adapted,  but  they  have 
been  kept  out  by  some  natural  barrier.  This  is  particu- 
larly evident  in  the  case  of  Australia,  where  the  weak  native 
animals  would  have  been  readily  displaced  by  the  stronger 
animals  of  Asia  could  these  have  reached  that  isolated  con- 
tinent. 

Life  on  Islands.  —  Islands  which  rise  from  the  conti- 
nental shelves  were  probably  at  one  time  connected  with 
the  continents,  but  have  since  been  separated  by  the  sub- 
mergence of  the  intervening  lowland.  The  animals  and 
plants  of  such  islands  are  similar  to  those  of  the  adjacent 
large  land  masses.  But  oceanic 
islands  possess  only  those  types 
of  plants  and  animals  which 
originally  were  able  to  float  or 
fly  to  them  over  the  surround- 
ing water  expanse.  Indigenous 
mammals,  except  certain  species 
of  bat,  are  wanting.  Birds  are 
abundant. 

On  the  tropical  islands  the 
cocoanut  palm  furnishes  the  main 
supply  of  vegetable  food,  cloth- 
ing, and  building  material.  Many  of  the  species  of  both 
plants  and  animals  are  different  from  those  of  'the  nearest 
continent  and  even  of  the  adjacent  islands.  So  complete 
has  been  the  isolation  of  the  life  on  these  islands  for  so  long 
a  time  that  it  has  been  possible  for  great  differences  in 
species  to  develop.  Large  unwieldy  birds  unable  to  fly  or 
run  rapidly  have  been  found  on  some  oceanic  islands,  the 


THE  DODO 

Although  the  dodo  is  extinct, 
sufficient  remains  have  been 
to 


LIFE  OF  MAN  AFFECTED  BY  PHYSICAL  FEATURES    541 

dodo   of  Mauritius,   now  extinct,   being  one  of   the  most 
notable. 

The  absence  of  predatory  animals  has  probably  made  the 
development  of  such  forms  possible.  The  great  species 
of  tortoise  from  the  Galapagos  Islands  perhaps  owes  its 
development  to  the  same  cause.  Nowhere  else  have  such 
huge  tortoises  been  found.  The  remarkable  fauna  and 
flora  found  on  oceanic  islands  may  be  regarded  as  due  to 
their  geographical  isolation. 

Life  of  Man  as  Affected  by  Physical  Features.  —  Moun- 
tains offer  a  retreat  to  persecuted  people  as  well  as  to  ani- 
mals. Here  are  often  found  the  races  which  once  inhabited 


HIGHLANDS 


the  surrounding  plains,  but  which  have  been  driven  from 
them  by  conquerors.  The  people  of  Wales  and  the  Scotch 
Highlanders  are  probably  descendants  from  more  ancient 
inhabitants  of  the  island  than  those  in  control  to-day.  The 


542      LIFE  AS   RELATED   TO  PHYSICAL  CONDITIONS 

Pyrenees,  the  Caucasus,  and  the  Himalaya  Mountains  each 
contain  tribes  which  were  driven  from  the  lower  plains, 
but  have  been  able  in  these  retreats  to  withstand  invaders 
who  were  too  powerful  for  them  in  their  former  homes. 

Old-fashioned  customs  still  maintain  their  hold  in  remote 
mountain  regions  long  after  they  have  been  discarded  in 
the  surrounding  country  where  intercommunication  is 
easier.  In  some  of  the  Scotch  Highlands  the  natives  still 


CRIPPLE  CREEK 
One  of  the  largest  mining  camps  in  the  world. 

cling  to  their  ancient  dress,  and  in  sections  of  the  southern 
Appalachian  Mountains  many  of  the  customs  of  the  early 
pioneers  are  still  common. 

In  mountain  regions  rich  in  ores,  mining  naturally  be- 
comes the  chief  industry,  and  here,  if  there  were  any  secluded 
native  inhabitants,  these  have  been  replaced  by  the  energetic 
miners  from  distant  places.  The  deep  and  remote  valleys 
and  mountain  sides  have  become  the  homes  of  mining 
camps  and  cities.  Railroads  have  been  built  to  these, 
overcoming  almost  impassable  obstructions,  and  ore  crush- 


EFFECT  OF  MOUNTAINS  ON  HISTORY          543 

ing  and  smelting  works  supply  the  places  of  the  mills  and 
factories  of  the  manufacturing  cities.  When  the  ore  fails, 
the  army  of  workers  moves  on,  and  the  city,  once  thriving 
and  booming,  becomes  suddenly  simply  an  aggregation  of 
empty  dwellings. 

Modern  irrigation  has  developed  many  barren  uplands 
into  wonderfully  successful  agricultural  districts. 

Effect  of  Mountains  on  History.  —  Not  only  have  moun- 
tains been  retreats  for  the  vanquished,  but  they  have  been 
barriers  against  further  conquest  by  the  conquerors.  It 
is  very  difficult  for  an  army  to  traverse  a  mountain  range. 
For  a  long  time  the  Alps  hemmed  in  the  power  of  Rome. 
One  of  the  greatest  exploits  of  Hannibal  and  later  of  Napo- 
leon was  the  passage  of  these  same  mountains. 

In  our  own  country  the  Appalachian  Mountains  acted 
for  a  long  time  as  an  impassable  barrier  to  the  expansion 
of  the  Thirteen  Colonies.  The  trails  across  them  were 
so  long  and  difficult  that  it  was  many  years  before  the  fer- 
tile plains  on  their  western  side  became  populated.  The 
Mohawk  valley  opened  a  comparatively  easy  route  at  the 
north,  but  the  Cumberland  trail  at  the  south  was  long, 
circuitous,  and  full  of  places  suitable  for  Indian  ambuscade. 

The  little  mountain  country  of  Switzerland  is  a  buffer 
state  for  the  rest  of  Europe.  Afghanistan,  rough,  moun- 
tainous, and  desert,  is  a  buffer  state  for  Asia.  It  may 
happen  that  mountain  boundaries  are  so  broad  and  compli- 
cated that  a  little  country  inserts  itself  along  the  boundary 
of  two  powerful  nations  and  is  able  to  protect  itself  from 
being  absorbed  by  either.  The  little  country  of  Andorra, 
containing  only  150  square  miles,  situated  in  a  lofty  valley 
on  the  southern  slope  of  the  Pyrenees,  with  a  population 


544      LIFE  AS  RELATED  TO  PHYSICAL  CONDITIONS 

not  exceeding  10,000,  has  remained  independent  for  nearly 
a  thousand  years  in  spite  of  its  powerful  neighbors. 

Life  on  Plains.  —  The  life  conditions  on  plains  are  very 
different  from  those  in  places  where  the  irregularities  of 
the  surface  are  great.  Movement  is  as  easy  in  one  direc- 
tion as  in  another,  and  the  lines  of  travel  tend  to  be  straight. 


A  HERD  OF  CATTLE  ON  THE  GREAT  PLAINS 

There  is  usually  no  reason  for  an  accumulation  of  popula- 
tion in  any  one  place,  so  the  population  tends  to  be  uni- 
formly distributed. 

As  movement  from  place  to  place  is  easy,  it  is  not  dif- 
ficult for  the  inhabitants  of  a  plain  to  mass  themselves 
together  at  one  point.  In  case  of  invasion  by  a  superior 
enemy  there  is  no  place  for  hiding  or  safe  retreat,  and  sub- 
jection or  extermination  are  the  alternatives,  unless  the 
plain  is  so  large  that  the  enemy  is  unable  to  spread  over 
it.  In  the  case  of  animals  this  has  been  shown  in  the  prac- 
tical extermination  of  the  American  bison  and  antelope. 


LIFE   ON   PLAINS 


545 


In  the  case  of  men  it  was  shown  on  the  plains  of  Russia 
in  the  thirteenth  century  when  the  Tartars  conquered  the 
region  and  threatened  to  overrun  Europe. 

Another  instance  was  that  of  the  fatal  invasion  of  Russia 
by  Napoleon.  The  Russians,  unable  to  find  a  strategic 
place  to  make  a  stand,  retreated  farther  and  farther  into 
the  plain.  The  depletion  of  Napoleon's  army,  due  to  the 


extent  of  territory  which  must  be  held  in  his  rear,  the  dis- 
tance from  his  base  of  supplies,  and  the  rigor  of  the  Russian 
winter,  forced  him  to  begin  that  disastrous  retreat,  the  fatal 
results  of  which  probably  led  to  his  final  overthrow. 

Plains  have  always  played  an  important  part  in  history. 
Here  armies  can  march  and  countermarch  with  compara- 
tive ease.  Large  bodies  of  men  can  easily  be  assembled. 
Military  stores  can  be  readily  collected  and  all  the  opera- 
tions of  war  carried  on  without  natural  obstructions.  Thus 


546      LIFE   AS   RELATED   TO  PHYSICAL  CONDITIONS 

it  happens  that  certain  plains  have  been  the  seats  of  almost 
innumerable  wars.  The  great  plain  of  the  Tigris  and  Eu- 
phrates was  the  gathering  ground  and  battlefield  of  vast 
ancient  monarchies.  The  plains  of  the  Po  have  been  the 
arena  in  which  embattled  Europe  has  settled  some  of  its 
deadliest  strifes,  while  the  level  lands  of  Belgium  have  been 
dyed  again  and  again  with  the  blood  of  thousands  and 


A  PART  OF  THE  PLAIN  OF  WATERLOO,  BELGIUM 

thousands  of  Europe's  bravest  sons.  The  brutal  invaders 
of  1914  cynically  admitted  that  they  overran  Belgium  be- 
cause it  was  the  shortest  and  easiest  military  route  to  Paris. 

Life  on  Coastal  Plains.  —  The  valuable  minerals  of  the 
earth  are  usually  found  in  the  older  rocks,  so  there  is  no 
mining  on  a  coastal  plain,  and  because  the  rivers  are  shal- 
low and  fall  over  no  ledges  as  they  flow  across  these  plains, 
no  great  water  power  for  manufacturing  can  be  developed. 
The  sluggish  streams  are  often  dammed  and  small  water 


LIFE   ON   COASTAL  PLAINS 


547 


powers  developed,  but  there  is  not  the  fall  necessary  for 
large  factories,  except  sometimes  in  the  hilly  region  back 
near  the  old  land  where  the  rivers  have  developed  rather 
deep  and  narrow  valleys,  and  mill  ponds  of  considerable 
size  may  be  made. 

As  the  different  kinds  of  soil  lie  in  belts,  agriculture  will 
vary  with  the  belts.  In  warm  climates  rice  can  be  raised 
along  the  shore  where  the  land  is  marshy.  On  the  sandy 
land  most  profitable 
truck  farming  is  pos- 
sible if  the  transpor- 
tation facilities  are 
good.  In  many 
places  in  the  south- 
ern states  these  sandy 
areas  support  fine 
forests  of  pine  (page 
344),  which  are  most 
valuable  for  the  pro- 
duction of  turpen- 
tine, tar,  and  lumber. 
Where  the  soil  is  not 

too  sandy  and  the  climate  is  warm,  cotton  is  raised  in 
abundance.  The  materials  for  making  glass,  pottery,  and 
brick  are  widespread  over  coastal  plains. 

The  cities  on  coastal  plains  are  usually  found  either 
(1)  near  the  coast,  where  the  rivers  have  formed  harbors 
and  so  have  made  ocean  commerce  possible,  or  (2)  at  the 
head  of  navigation  in  the  rivers  where  water  transporta- 
tion begins,  or  (3)  still  farther  up  the  river  at  the  fall  line, 
where  manufacturing  on  a  large  scale  is  possible. 

The  fall  line  is  the  point  on  a  river  where  its  bed  passes 


CRUDE  TURPENTINE  STILL 

Turpentine  is  distilled  from  the  pitch  of 
the  pine. 


548      LIFE  AS  RELATED   TO   PHYSICAL  CONDITIONS 

from  the  harder  rock  of  the  old  land  to  the  softer  material 
of  the  coastal  plain.  The  softer  material  is  worn  away  more 
easily  than  the  hard  material,  and  falls  or  rapids  are  pro- 
duced suitable  for  water  power.  A  glance  at  a  map  of 
the  southeastern  United  States  will  show  that  the  princi- 
pal cities  lie  in  line  nearly  parallel  to  the  coast.  Of  those 


PINEAPPLES 

near  the  coast  are  Norfolk,  Wilmington,  Charleston,  Sa- 
vannah, Jacksonville;  at  the  fall  line,  Trenton,  Phila- 
delphia, Richmond,  Columbia,  and  Augusta. 

Advantages  of  Harbors.  —  The  importance  to  mankind 
of  good  harbors  cannot  be  overestimated.  The  latest  and 
greatest  of  all  wars  has  especially  emphasized  this.  Thou- 
sands and  thousands  of  men  have  been  sacrificed  in  efforts 
to  obtain  or  to  defend  harbors. 

No  civilized  country  by  its  own  products  can  supply  all  the 
wants  of  its  inhabitants.  Since  earliest  times  man  has  been 


ADVANTAGES  OF  HARBORS 


549 


a  barterer  of  goods.  The  sea  offers  him  an  unrestricted 
highway  for  his  traffic.  Harbors  he  must  have  to  load  and 
unload  his  wares  safely. 

Although  many  of  the  best  harbors  of  the  world  are 
found  along  depressed  coasts,  such  as  the  harbors  of  New 
York,  San  Francisco, 
London,  Liverpool, 
and  Bergen,  yet  there 
are  several  other 
sorts  of  harbors. 
The  delta  of  a  great 
river  may  afford  a 
good  harbor,  as  those 
of  New  Orleans  and 
Calcutta.  Harbors 
may  be  formed  by 
sand  reefs  and  spits, 
like  those  of  Calves-* 
ton,  Provincetown, 
and  San  Diego.  The 
atolls  of  the  mid- 
Pacific  and  even  the 
submerged  craters  of 
volcanic  islands  af- 
ford safe  resting 
places  where  ships 
may  ride  out  the 
storms. 

All  natural  fea- 
tures have  a  greater 
or  less  influence  upon 
the  inhabitants  of  of  Boston. 


Minor's  LEDGE  LIOHTHOUSK 
Situated  on  a  reef  about  15  miles  southeast 


550     LIFE  AS  RELATED  TO  PHYSICAL  CONDITIONS 

the  earth,  but  perhaps  none  has  so  directly  and  obviously 
influenced  man's  activities  as  has  the  kind  of  coast  on 
which  he  lives.  Europe,  with  its  harborful,  and  Africa 
with  its  almost  harborless  coasts  are  in  striking  contrast 
to  each  other.  This  difference  between  the  inducements 


SAN  FRANCISCO  HARBOR, 
A  harbor  due  to  a  depression  of  the  coast. 

to  travel  and  commerce  which  the  two  continents  afford 
is  one  of  the  factors  in  producing  the  marked  difference 
in  progress  attained  by  the  native  peoples  of  the  two  con- 
tinents. They  stand  to-day  .as  types  on  the  one  hand  of 
economic  progress  and  on  the  other  of  stagnation. 

The    Phoenicians,    the    Carthaginians,    the    Greeks,    the 
English,  and   the  other  great   nations  of  the   world  have 


ADVANTAGES  OF  HARBORS 


551 


felt  the  enticing  allurement  of  a  captive  sea  waiting  in 
their  harbors  like  a  steed  for  them  to  mount  and  ride  away 
in  quest  of  the  world's  best.  Thus  they  have  extended 
their  conquest  and  influence  far  beyond  the  homeland. 
All  nations  regard  adequate  outlet  to  the  sea  as  essential 


CALIFORNIA,  U.  S.  A. 

One  of  the  finest  harbors  in  the  world. 

to  progress.  The  struggle  of  all  the  great  world  powers  to 
strengthen  their  navies,  no  matter  what  the  cost,  shows 
with  what  jealousy  the  products  of  their  ports  are  guarded. 
Coasts  with  harbors  give  their  people  the  facilities  and 
inducements  for  seeking  the  unknown,  while  the  harbor- 
less  coasts  confine  the  aspirations  of  their  inhabitants  to 
the  products  immediately  around  them.  A  glance  at  the 


552      LIFE   AS  RELATED   TO   PHYSICAL  CONDITIONS 

coast  line  and  harbors  of  Greece  shows  one  cause  of  its 
ancient  civilization  and  a  reason  why  the  Greeks  were 
"  always  seeking  some  new  thing." 


SUMMARY 

Physical  conditions  have  a  great  effect  on  the  distribution 
of  life  upon  the  earth.  It  is  hard  for  living  things  to  cross 
high  mountains,  broad  oceans,  or  vast  deserts.  When  con- 
fined to  certain  climates  and  areas,  plants  and  animals 
naturally  adjust  themselves  to  these. 

Life  in  the  sea  is  so  simple  that  plants  and  animals  there 
are  not  forced  to  become  as  highly  developed  as  are  those 
of  the  land.  On  land  there  are  greater  ranges  of  climate 
and  other  physical  conditions,  so  that  plants  and  animals 
have  been  forced  to  a  high  development  in  order  to  survive. 
Man  is  one  of  the  greatest  forces  at  present  affecting  land 
life.  He  transplants  and  transports  animals  and  plants 
according  to  his  desires.  The  physical  conditions  decide 
whether  or  not  they  shall  live. 

The  elevation  of  mountain  regions,  difficulty  of  travel, 
and  lack  of  agricultural  lands  cause  these  sections  to  be 
sparsely  settled  by  backward  peoples  unless  mining  has 
attracted  progressive  settlers.  Mountains  have  always 
furnished  safe  retreats  for  persecuted  peoples  and  have  been 
barriers  to  further  conquest. 

Life  on  the  plains  is  usually  most  varied.  But  since  the 
plains  offer  no  safe  retreat,  the  inhabitants  of  level  lands 
have  always  been  subject  to  invasion  and  conquest,  and  the 
native  animals  to  extermination.  Coastal  plains  offer  no  op- 
portunities for  mining,  but  certain  kinds  of  manufacturing  and 
agricultural  pursuits  are  peculiar  to  such  regions.  Access  to 


QUESTIONS  553 

the  sea,  which  is  the  oldest  and  easiest  highway,  is  essential 
to  the  progress  of  a  nation. 

QUESTIONS 

What  do  the  rock  layers  show  in  regard  to  the  history  of  life? 

Give  several  reasons  why  the  same  kinds  of  plants  and  animals 
are  not  found  all  over  the  earth. 

How  has  the  glacial  period  affected  plants  and  animals  and 
man's  activities? 

What  plants  and  animals  do  you  know  that  are  particularly 
adapted  to  the  conditions  in  which  they  live? 

How  does  the  lif e  of  the  sea  differ  from  that  of  the  land  ? 

How  has  the  distribution  of  animals  been  affected  by  geographical 
conditions  ? 

How  have  different  physical  features  of  the  earth  affected 
life  and  history? 


APPENDIX 

Units.  —  To  measure  any  physical  quantity  a  certain 
definite  amount  of  the  same  kind  of  quantity  is  used  as  the 
unit.  For  example,  to  measure  the  length  of  a  body,  some 
arbitrary  length,  as  a  foot,  is  chosen  as  the  unit  of  length ; 
the  length  of  a  body  is  the  number  of  times  this  unit  is  con- 
tained in  the  longest  dimension  of  the  body.  The  unit  is 
always  expressed  in  giving  the  magnitude  of  any  physical 
quantity ;  the  other  part  of  the  expression  is  the  numerical 
value.  For  example,  60  feet,  500  pounds,  45  seconds. 

In  like  manner,  to  measure  a  surface,  the  unit,  or  stand- 
ard surface,  must  be  given,  such  as  a  square  foot ;  and  to 
measure  a  volume,  the  unit  must  be  a  given  volume,  such, 
for  example,  as  a  cubic  inch,  a  quart,  or  a  gallon. 

Systems  of  Measurement.  —  Commercial  transactions  in 
most  civilized  countries  are  carried  on  by  a  decimal  system 
of  money,  in  which  all  the  multiples  are  ten.  It  has  the 
advantage  of  great  convenience,  for  all  numerical  operations 
in  it  are  the  same  as  those  for  abstract  numbers  in  the  dec- 
imal system.  The  system  of  weights  and  measures  in  use 
in  the  British  Isles  and  in  the  United  States  is  not  a  dec- 
imal system,  and  is  neither  rational  nor  convenient.  On 
the  other  hand  most  of  the  other  civilized  nations  of  the 
world  within  the  last  fifty  years  have  adopted  the  nn-tric 
system,  in  which  the  relations  are  all  expressed  by  some 
power  of  ten.  The  metric  system  is  in  well-nigh  universal 
use  for  scientific  purposes.  It  furnishes  a  common  nuuu-r- 
ical  language  and  greatly  reduces  the  labor  of  computation. 
555 


556  EVERYDAY  SCIENCE 

Measure  of  Length.  —  In  the  metric  system  the  unit 
of  length  is  the  meter.  In  the  United  States  it  is -the  dis- 
tance between  two  transverse  lines  on  each  of  two  bars  of 
platinum-iridium  at  the  temperature  of  melting  ice.  These 
bars,  which  are  called  "  national  prototypes,"  were  made 
by  an  international  commission  and  were  selected  by  lot 
after  two  others  had  been  chosen  as  the  "  international  pro- 
totypes "  for  preservation  in  the  international  laboratory 
on  neutral  ground  at  Sevres  near  Paris.  Our  national 
prototypes  are  preserved  at  the  Bureau  of  Standards  in 
Washington.  The  two  ends  of  one  of  them  are  shown  below. 
The  only  multiple  of  the  meter  in  general  use  is  the  kilo- 
meter, equal  to  1000  meters.  It  is  used  to  measure  such 
distances  as  are  expressed  in  miles  in  the  English  system. 


ENDS  OF  Mi 

The  Common  Units  in  the  Metric  System  are 

1  kilometer  (km.)  =  1000  meters  (m.) 

1  meter  =  100  centimeters  (cm.) 

1  centimeter  =  10  millimeters  (mm.) 

The  Common  Units  in  the  English  System  are : 

1  mile  (mi.)   =  5280  feet  (ft.) 

1  yard  (yd.)  =  3  feet 

1  foot  =  12  inches  (in.) 

By  Act  of  Congress  in  1866  the  legal  value  of  the  yard 
is  ffff  meter ;  conversely  the  meter  is  equal  to  39.37  inches. 
The  inch  is,  therefore,  equal  to  2.540  centimeters. 


APPENDIX  557 

The  unit  of  length  in  the  English  system  for  the  United 
States  is  the  yard,  defined  as  above.  The  relation  between 
the  centimeter  scale  and  the  inch  is  shown  below. 

100  MILLIMETERS  =  10  CENTIMETERS  =  1  DECIMETER  =  3.  93T  INCHES. 


1  1  1  1  1  1  1 

1  1  1  1  1  1  1  1  1  1  1  1)  1 

TTjilTf 

1  .  :  l 

1  1  1  1  1  1  1  I  1  1  1  1 

1  1  I  1     1  I  1  1  II  1  1  I  II  1  1  1  11  1  I  I  1  I  1  I  1  1  1  II  1  1  II 

1  II  1  ill  1  Ml 

1 

1   1 

O_I  .. 

2 

1            1      1      |     1      1      1      1      |      I      1      1      1 

g 

III!] 

INCHES  AND  TENTHS 

CENTIMETER  AND  INCH  SCALES 


Measures  of  Surface.  —  In  the  metric  system  the  unit 
of  area  used  in  the  laboratory  is  the  square  centimeter 
(cm.2).  It  is  the  area  of  a  square  the  edge  of  which  is 
one  centimeter.  The  square  meter  (m.2)  is  often  employed 
as  a  larger  unit  of  area.  In  the  Eng- 
lish system  both  the  square  inch  and  the 
square  foot  are  in  common  use.  Small 
areas  are  measured  in  square  inches,  while 
the  area  of  a  floor  and  that  of  a  house  lot 
are  given  in  square  feet  ;  larger  land  areas 
are  in  acres,  640  of  which  are  contained  in 

SQUARE  CENTIMKTI  it 

a  square  mile.  AND  SQUARK  IVH 

The  square  inch  contains  2.54  X  2.54 
:  =  6.4516  square  centimeters.    The  relative  sizes  of  tin-  t\v. 
are  shown  in  the  accompanying  figure. 

The  area  of  regular  geometric  figures  is  obtained  by  computation 
from  their  linear  dimensions.     Thus  the  area  of  a  rectangle  or  of  a 
parallelogram  is  equal  to  the  product  of  its  basr  ami  iti  ittftade 
\(A  =  b  X  K)  ;  the  area  of  a  triangle  is  half  the  product  of  it 
and  its  altitude  (A  =  &  X  h)  ;  the  area  of  a  circle  is  the  pro 
3.1416  (very  nearly  V-)  and  the  square  of  the  radius  (. 
the  surface  of  a  sphere  is  four  times  the  area  of  a  circle  throi 
center  (A  =  47rr2). 


558 


EVERYDAY   SCIENCE 


CUBIC  CENTIMETER  AND 
CUBIC  INCH 


Cubic  Measure.  —  The  smaller  unit  of  volume  in  the 
metric  system  is  the  cubic  centimeter.  It  is  the  volume  of 
a  cube  the  edges  of  which  are  one  centimeter  long.  The 
cubic  inch  equals  (2.54)3  or  16.387 
cubic  centimeters.  The  relative  sizes 
of  the  two  units  are  shown  here. 
In  the  English  system  the  cubic  foot 
and  cubic  yard  are  employed  for  larger 
volumes.  The  cubical  capacity  of  a 
room  or  of  a  freight 
car  would  be  ex- 
pressed in  cubic  feet ; 
the  volume  of  build- 
ing sand  and  gravel  or  of  earth  embank- 
ments, cuts,  or  fills  would  be  in  cubic  yards. 
The  unit  of  capacity  for  liquids  in  the 
metric  system  is  the  liter.  It  is  a  decimeter 
cube,  that  is,  1000  cubic  centimeters.  The 
imperial  gallon  of  Great  Britain  contains 
about  277.3  cubic  inches,  and  holds  10 
pounds  of  water  at  a  temperature  of  62° 
Fahrenheit.  The  United  States  gallon  has 
the  capacity  of  231  cubic  inches. 

Common  Units  in  the  Metric  System : 

1  cubic  meter  (m.3)       =  1000  liters  (1.) 

1  liter  =  1000  cubic  centimeters  (cm.3) 

Common  Units  in  the  English  System : 

1  cubic  yard  (cu.  yd.)  =  27  cubic  feet  (cu.  ft.) 

1  cubic  foot  =  1728  cubic  inches  (cu.  in.) 

1  U.  S.  gallon  (gal.)      =  4  quarts  (qt.)  =  231  cubic  inches 

1  quart  =  2  pints  (pt.) 


CYLINDRICAL  GLASS 
GRADUATE 


APPENDIX 


559 


The  volume  of  a  regular  solid,  or  of  a  solid  geometrical  figure,  may 
be  calculated  from  its  linear  dimensions.  Thus,  the  number  of  cubic 
feet  in  a  room  or  in  a  rectangular  block  of  marble  is 
found  by  getting  the  continued  product  of  its  length, 
its  breadth,  and  its  height,  all  measured  in  feet.  The 
volume  of  a  cylinder  is  equal  to  the  product  of  the  area 
of  its  base  (irr2)  and  its  height,  both  measured  in  the 
same  system  of  units. 

Liquids  are  measured  by  means  of  graduated  vessels 
of  metal  or  of  glass.  Thus,  tin  vessels  holding  a  gal- 
lon, a  quart,  or  a  pint  are  used  for  measuring  gasoline, 
sirup,  etc.  Bottles  for  acids  usually  hold  either  a 
gallon  or  a  half  gallon,  and  milk  bottles  contain  a 
quart,  a  pint,  or  a  half  pint.  Glass  cylindrical  grad- 
uates and  volumetric  flasks  are  used  by  pharma- 
cists, chemists,  and  physicists  to  measure  liquids. 
In  the  metric  system  these  are  graduated  in  cubic  VOLUMETRIC 
centimeters.  MASK 

Units  of  Mass.  —  The  unit  of  mass  in  the  metric  system 
is  the   kilogram.     The   United   States  has  two  prototype 

kilograms  made  of 
platinum-iridium  and 
preserved  at  the  Bureau 
of  Standards  in  Wash- 
ington. The  gram  is 
one  thousandth  of  the 
kilogram.  The  latter 
was  originally  designed 
to  represent  the  mass 
of  a  liter  of  pure  water 
at  4°  C.  (centigrade 
scale).  For  practical 
purposes  this  is  the 

STANDARD  KILOGBAM  kilogram.     The  gram  is 


i 


560  EVERYDAY   SCIENCE 

therefore  equal  to  the  mass  of  a  cubic  centimeter  of  water  at 
the  same  temperature.  The  mass  of  a  given  body  of  water 
can  thus  be  immediately  inferred  from  its  volume. 

The  unit  of  mass  in  the  English  system  is  the  avoirdupois 
pound.  The  ton  of  2000  pounds  is  its  chief  multiple ;  its 
submultiples  are  the  ounce  and  the  grain.  The  avoirdupois 
pound  is  equal  to  16  ounces  and  to  7000  grains.  The  "  troy 
pound  of  the  mint  "  contains  5760  grains.  In  1866  the  mass 
of  the  5-cent  nickel  piece  was  legally  fixed  at  5  grams ;  and 
in  1873  that  of  the  silver  half  dollar  at  12.5  grams.  One 
gram  is  equal  approximately  to  15.432  grains.  A  kilogram 
is  very  nearly  2.2  pounds.  More  exactly,  one  kilogram 
equals  2.20462  pounds. 

All  mail  matter  transported  between  the  United  States  and  the 
fifty  or  more  nations  signing  the  International  Postal  Convention, 
including  Great  Britain,  is  weighed  and  paid  for  entirely  by  metric 
weight.  The  single  rate  upon  international  letters  is  applied  to  the 
standard  weight  of  15  grams  or  fractional  part  of  it.  The  Inter- 
national Parcels  Post  limits  packages  to  5  kilograms;  hence  the 
equivalent  limit  of  11  pounds. 

Common  Units  in  the  English  System  : 

1  ton  (T.)  =  2000  pounds  (Ib.) 
1  pound      =16  ounces  (oz.) 
1  ounce       =  437.5  grains  (gr.) 

Common  Units  in  the  Metric  System  : 

1  kilogram  (kg.)  =  1000  grams  (g.) 

1  gram  =  1000  milligrams  (mg.) 

The  Unit  of  Time.  —  The  unit  of  time  in  universal  use 
in  physics  and  by  the  people  is  the  second.     It  is  sa 
of  a  mean   solar  dav.     The   number  of   seconds  between 


APPENDIX  561 

the  instant  when  the  sun's  center  crosses  the  meridian  of 
any  place  and  the  instant  of  its  next  passage  over  the  same 
meridian  is  not  uniform,  chiefly  because  the  motion  of  the- 
earth  in  its  orbit  about  the  sun  varies  from  day  to  day. 
The  mean  solar  day  is  the  average  length  of  all  the  variable 
solar  days  throughout  the  year.  It  is  divided  into  24  X 
60  X  60  =  86,400  seconds  of  mean  solar  time,  the  time  re- 
corded by  clocks  and1  watches.  The  sidereal  day  used  in 
astronomy  is  nearly  four  minutes  shorter  than  the  mean 
solar  day. 

The  Three  Fundamental  Units.  —  Just  as  the  measure- 
ment of  areas  and  of  volumes  reduces  simply  to  the  measure- 
ment of  length,  so  it  has  been  found  that  the  measurement 
of  most  other  physical  quantities,  such  as  the  speed  of  a  ship, 
the  pressure  of  water  in  the  mains,  the  energy  consumed  by 
an  electric  lamp,  and  the  horse  power  of  an  engine,  may  be 
made  in  terms  of  the  units  of  length,  mass,  and  time.  For 
this  reason  these  three  are  considered  fundamental  units 
to  distinguish  them  from  all  others,  which  are  called  derived 
units. 

The  system  now  in  general  use  in  the  physical  sciences 
employs  the  centimeter  as  the  unit  of  length,  the  gram  as 
the  unit  of  mass,  and  the  second  as  the  unit  of  time.  It 
is  accordingly  known  as  the  c.  g.  s.  (centimeter-gram-second) 
system. 


PROJECTS 

PROJECT  I.  —  How  a  Boy  Scout  Determines  Directions  by  the  Stars, 
pages  9  and  10 

Determining  directions  by  the  stars  requires  a  little  practice. 
The  necessary  information  may  be  found  on  pages  9  and  10  of 
the  body  of  the  book.  When  you  are  hi  some  locality  where  you 
know  the  points  of  the  compass,  turn  to  the  northern  sky  on  a 
clear  night  and  see  if  you  can  locate  the  Big  Dipper  (Diagram, 
p.  10). 

Remember  that  the  stars  in  the  north  appear  to  go  around  in  a 
circle  once  every  twenty-four  hours  (p.  8),  and  so  you  may  find  the 
Big  Dipper  near  the  zenith  (the  point  of  the  sky  directly  overhead), 
down  near  the  horizon,  or  somewhere  on  its  circuit  between  these 
two  points.  Rotate  the  diagram  on  page  10  about  Polaris  as  a 
center,  and  you  will  observe  all  the  relative  positions  to  the  North 
Star  which  the  Big  Dipper  may  occupy. 

If  you  live  in  the  southern  portion  of  the  United  States,  part  of 
the  Big  Dipper  may  disappear  below  the  horizon  when  the  con- 
stellation swings  below  the  North  Star;  but  the  "pointers"  are 
generally  in  sight.  If  you  will  follow  the  direction  indicated  by 
these  "pointers,"  as  shown  in  the  diagram  on  page  10,  you  will 
find  Polaris  very  easily.  It  is  a  lonesome-looking  star,  because  ii  is 
fairly  bright  and  is  surrounded  by  stars  of  lesser  brilliance.  To 
identify  it  further,  see  if  you  can  trace  the  Little  Dipper.  The 
North  Star  forms  the  tip  end  of  the  handle  (Diagram,  p.  10). 

Now  see  if  you  can  locate  the  constellation  of  Cassiopeia's  Chair. 
It  is  about  as  far  from  the  North  Star  as  the  Big  Dipper  and  always 
on  the  opposite  side  of  Polaris  from  that  constellation  (Diagram, 
p.  10).  Above  the  North  Star,  it  is  M-shaped  ;  below  Polaris,  it 
is  inverted  into  a  W-shaped  cluster. 
563 


564  EVERYDAY  SCIENCE 

Learn  to  recognize  these  three  northern  constellations  so  that 
you  can  trace  them  readily,  and  you  will  be  able  to  locate  the  North 
Star  without  difficulty.  Then  when  you  are  in  a  strange  locality, 
the  northern  sky  will  seem  familiar  to  you  and  will  guide  you 
unerringly. 

When  you  have  located  the  North  Star,  face  it  with  arms  out- 
stretched to  right  and  left.  The  right  arm  points  to  the  east ; 
the  left  arm  to  the  west. 

PROJECT  II.  —  How  a  Boy  Scout  Determines  Directions  by  Day, 
pages  23,  24,  37,  38 

(a)  To  determine  directions  with  the  aid  of  a  watch,  point  the 
hour-hand  toward  the  sun.  To  do  this  accurately,  hold  the  watch, 
face  upward,  in  the  palm  of  your  hand.  Hold  a  match  or  a  straight 
twig  upright  at  the  edge  of  the  dial  and  turn  the  watch  until  the 
hour-hand  points  toward  the  match  and  the  shadow  of  the  match 
lies  directly  along  the  line  of  the  hour-hand. 

The  point  on  the  dial  halfway  between  the  hour-hand  and  the 
figure  XII  will  then  indicate  south  with  a  fair  degree  of  accuracy. 
Thus,  if  the  hour-hand  is  at  X,  the  figure  XI  on  the  dial  will  point 
toward  the  south ;  if  the  hour-hand  is  at  III,  the  mark  on  the  dial 
that  indicates  1 :  30  will  point  toward  the  south. 

EXPLANATION.  —  The  reason  for  this  is  that  on  a  day  of  average 
length  (twelve  hours)  the  sun  appears  to  describe  a  half-circle  in  the 
sky  while  the  hour-hand  of  your  watch  is  describing  a  complete  circle. 
If  the  watch  and  the  sun  both  described  a  semicircle  in  the  same  length 
of  time,  the  figure  XII  would  always  point  toward  the  south  if  the  hour- 
hand  were  aimed  at  the  sun.  But  since  the  hour-hand  travels  its  cir- 
cuit twice  as  fast  as  the  sun,  it  is  necessary  to  halve  the  distance  between 
the  hour-hand  and  the  figure  XII  in  order  to  find  the  point  on  the  dial 
that  indicates  the  south. 

(6)  A  reliable  pocket  compass  may  be  had  for  a  reasonable  sum. 
Learn  from  some  surveyor  the  declination  (p.  38)  for  your  imme- 
diate section  so  that  you  may  determine  the  true  north  accurately. 
You  may  purchase  magnetic  charts  from  the  United  States  Geolog- 


PROJECTS  565 

ical  Survey  which  will  show  the  variation  for  any  section  accurately. 
Only  be  sure  that  you  have  the  latest  issue  of  the  chart,  because  the 
declination  of  the  needle  slowly  changes  from  time  to  time  (pp. 
38,  39). 

Set  your  compass  in  a  place,  as  nearly  level  as  possible,  away 
from  the  vicinity  of  steel  and  iron.  Then  allow  for  the  declination 
and  you  will  have  the  true  north. 

If  you  cannot  afford  a  compass,  make  one  as  suggested  in  Exper- 
iment 8,  pages  37  and  38.  To  use  this  satisfactorily,  you  will  have 
to  train  your  eye  to  gauge  the  declination.  This  you  can  do  by 
floating  the  cork  compass  at  the  side  of  a  manufactured  compass 
as  often  as  you  have  opportunity.  Train  the  eye  to  recognize  the 
declination  of  the  floating  compass  by  comparing  it  with  the 
measured  declination  on  the  manufactured  compass. 

Put  the  cork  in  your  pocket  and  carry  the  magnetized  needle  in  a 
small  glass  phial.  You  can  set  this  compass  wherever  there  is 
water. 

(c)  Hard  and  fast  rules  for  telling  direction  by  the  growth  of 
mosses  and  lichens  and  other  vegetation  in  forests  are  responsible 
for  a  good  deal  of  current  misinformation.  Writers  sometimes  give 
specific  information  for  certain  regions,  and  amateur  woodsmen 
get  the  impression  that  the  instructions  are  true  for  all  times  and 
places. 

Practiced  guides,  like  the  Indians  of  old,  can  tell  direction  within 
a  very  few  degrees  of  perfect  accuracy  by  observing  forest  vege- 
tation. This  ability  comes  of  long  and  acute  observation  and  can- 
not be  cultivated  by  rule.  A  few  basic  facts  may  be  given,  along 
with  advice  that  accurate  information  for  any  section  can  come 
only  of  close  observation  and  reasoning. 

As  a  rule,  mosses  and  lichens  grow  on  the  cool  or  shady  side 
of  a  tree.  In  the  North  Temperate  zone,  this  is  generally  the  nortl 
ern  side  but  it  may  vary  with  the  immediate  surroundings  and  with 
the  direction  of  the  prevailing  winds  and  rains.  For  instance, 
trees  growing  on  a  north  slope,  where  the  sun  ha*  no  arm*  to  tlx-ni, 
are  coolest  and  dampest  on  the  side  toward  the  ground,  and  may 
therefore  have  moss  on  the  south  side. 


566  EVERYDAY  SCIENCE 

To  offset  this  cause  of  confusion,  it  is  well  to  remember  that  in 
such  sections  underbrush  and  small  plants  grow  more  densely  on  a 
northern  exposure  than  on  a  southern  exposure,  because  the  sun 
does  not  get  a  chance  to  dry  out  the  north  slope  so  thoroughly. 
The  practiced  guide  knows  too  that  mosses  grow  where  they  can 
have  not  only  shade  but  an  abundance  of  moisture.  The  prevail- 
ing winds,  therefore,  may  have  something  to  do  with  local  variation 
of  moss  growths. 

If  you  are  near  a  forest,  make  a  study  of  conditions  that  prevail 
there  and  report  on  them  to  the  class.  Take  your  compass  with 
you.  Find  out  on  which  side  of  trees  the  moss  growths  usually 
occur.  If  not  on  the  north  side  at  all  times,  see  if  you  can  offer  a 
reason  for  the  variation.  Study  the  vegetation  and  soil  on  all  slopes, 
if  you  are  in  a  hilly  or  mountainous  region,  and  report  the  results 
of  your  observations. 

If  you  will  be  constantly  on  the  alert,  in  whatever  sections 
you  traverse,  you  will  eventually  accumulate  much  valuable  forest 
lore. 

PROJECT  III.  —  How  a  Boy  Scout  Determines  Latitude  by  the  North 
Star,  page  32 

Choose  a  straight  post  or  tree  from  which  the  North  Star  may  be 
sighted.  Nail  a  smooth  piece  of  board,  about  a  foot  square,  to  the 
east  or  west  side  of  the  post  or  tree  so  that  you  can  sight  the  North 
Star  along  the  face  of  the  board. 

Drive  a  six-penny  or  eight-penny  wire  nail  straight  and  securely 
into  the  upper  north  corner  of  the  face  of  the  board  (K),  and  sus- 
pend a  plumb  line  from  the  nail  (KL).  Now  from  the  south  edge 
of  the  board,  sight  along  the  face  of  it  until  you  can  see  the  North 
Star  immediately  under  the  wire  nail.  Then  move  the  point  of  a 
knife,  or  scratch-awl,  along  the  face  of  the  board  near  your  eye  until 
you  can  just  sight  the  North  Star  over  the  edge  of  the  blade.  When 
the  knife  reaches  this  spot,  stick  the  point  of  the  knife-blade  care- 
fully into  the  board.  If  you  have  sighted  accurately,  the  star  can 
be  seen  just  under  the  nail  and  over  the  knife  blade.  If  the  eye 


PROJECTS 


567 


be  moved  ever  so  little  up  or  down,  either  the  nail  or  the  knife- 
blade  will  cut  off  the  light  of  the  star. 

Now  you  are  ready  to  draw  three  lines  on  the  face  of  the  board, 
and  you  probably  will  need  an  artificial  light.  With  a  ruler,  draw 
a  line  exactly  corresponding  to  the  plumb  line  (KL).  Then  draw 


FlGUKB    1 

a  straight  line  from  the  point  of  the  nail  to  the  edge  of  the  knife 
blade  (KT).  With  a  carpenter's  square,  draw  a  line  (77))  at  right 
angles  to  the  plumb  line.  The  number  of  degrees  in  the  angle  at  T 
will  be  approximately  equal  to  your  latitude.  If  you  haven't  a 
protractor  to  measure  this  angle,  take  the  board  to  the  laboratory 
and  measure  the  angle. 

EXPLANATION.  —  If  we  could  draw  a  line  from  the  center  of  the 
earth  to  the  point  where  we  stand  (KL,  Figure  2),  we  should  have  a 
line  running  "straight  down"  (p.  24).  Since  the  weight  of  a  plumb 
line  points  to  the  center  of  the  earth,  the  direction  of  the  plumb  line 


568 


EVERYDAY  SCIENCE 


(KL,  Figure  1)  is  "straight  down."  Now  if  a  line  should  be  drawn  at 
the  earth's  surface  (TD,  Figure  2)  at  right  angles  to  the  first  line,  it 
would  indicate  our  horizon,  or  line  of 
vision  along  the  earth's  surface.  The 
line  TD  on  the  board  (Figure  1)  is  drawn 
at  right  angles  to  the  plumb  line  and 
-D  may,  therefore,  be  regarded  as  our  horizon 
line. 

Now  suppose  we  were  standing  at  the 
north  pole  (A",  Figure  2).  The  North 
Star  would  be  directly  overhead,  and  the 
line  of  light  from  the  star  to  the  eye 
(K — N-S,  Figure  2)  would  be  at  right 
angles,  90°,  to  our  horizon  line  (TD,  Fig- 
ure 2).  Thus  the  angle  of  the  North  Star 
above  the  horizon  line  at  the  north  pole,  90°, 
equals  the  latitude  of  the  north  pole,  90°. 
Suppose  we  should  travel  along  a  meridian  line  to  a  point  midway 

between  the  north  pole  and  the  equator,  45°  latitude  (K,  Figure  3). 

The  North  Star  would  no  longer  be  overhead,  but  would  be  about  half- 


FIGURE  2 


FIGURE  3 


FIGURE  4 


way  between  the  zenith  and  the  horizon.  The  line  of  light  from  Polaris 
to  the  eye  (K — N-S,  Figure  3)  would,  therefore,  form  about  half  a  right 
angle,  45°,  with  our  horizon  line  (TD). 

Suppose  we  should  travel  on  to  the  equator,  0°  latitude  (K,  Figure 
4).     The  North  Star  would  then  be  on  the  horizon.     The  line  of  light 


PROJECTS  569 

from  it  (K—N-S,  Figure  4)  would  be  identical  with  the  horizon  line 
(TD),  and  there  would  be  no  angle,  0°.  From  this  it  can  be  seen  that, 
in  order  to  measure  our  latitude,  we  need  only  measure  the  angle  of 
the  North  Star  above  the  horizon. 

Your  calculations  may  be  as  much  as  one  degree  off,  one  way  or  the 
other.  But  if  you  will  make  your  observations  on  a  night  when  the 
constellation  of  Cassiopeia  is  just  as  high  above  the  horizon  as  the 
North  Star,  you  will  get  accurate  results.  See  the  "  Boy  Scouts1  Hand- 
book," p.  96,  and  Figure  I,  on  page  10  of  this  book,  and  report  on  this 
to  the  class. 

PROJECT  IV.  —  Star  Projects  Varying  with  the  Seasons,  pages  1-18 

The  two  other  constellations  in  the  northern  heavens  that  are 
shown  in  the  diagram  on  page  10  are  Cepheus  and  the  Dragon 
(Draco) .  After  you  are  able  to  locate  with  certainty  the  other  three 
constellations  we  have  talked  about,  you  will  probably  be  able  to 
trace  these  two  constellations. 

Two  of  the  best  known  stars  in  the  northern  heavens  are  Vega 
and  Arcturus.  The  two  stars  forming  the  inside  edge  of  the  Big 
Dipper  next  to  the  handle  form  a  line  which  points  past  the  head 
of  the  Dragon  toward  a  large,  brilliantly  white  star.  This  is  Vega. 
The  two  stars  that  form  the  bottom  of  the  Little  Dipper  form  a 
line  pointing  away  from  the  Pole  toward  a  very  bright  reddish  star 
of  the  first  magnitude.  This  is  Arcturus,  mentioned  on  page  7 
of  this  book. 

Since  the  earth,  by  reason  of  its  revolution  around  the  sun  as 
well  as  its  rotation,  gradually  changes  its  position  in  relation  to  the 
stars,  there  is  a  noticeable  change  of  the  evening  sky  map  from  month 
to  month.  The  best  way  to  make  a  study  of  the  evening  sky  for 
any  particular  month  is  to  obtain  a  copy  of  the  "Monthly  Evening 
Sky  Map," l  a  little  journal  for  amateur  astronomers.  By  means 
of  this,  from  month  to  month,  you  may  identify  the  planets,  im- 
portant constellations  (such  as  Scorpio,  in  midsummer ;  and  Orion, 
in  midwinter)  and  important  stars,  including  Sirius,  the  Dog-Star, 

1  "The  Monthly  Evening  Sky  Map,"  Leon  Barritt,  Publisher,  367 
Fulton  Street,  Brooklyn,  New  York. 


570  EVERYDAY  SCIENCE 

the  brightest  star  in  the  heavens,  which  appears  low  on  the  southern 
horizon  in  midwinter. 

Among  the  many  interesting  books  on  the  study  of  the  stars  are 
the  following : 

"Earth  and  Sky  Every  Child  Should  Know,"  Rogers.  Double- 
day,  Page  &  Co. 

"Easy  Star  Lessons,"  Proctor.    G.  P.  Putnam's  Sons,  New  York. 

"The  'Book  of  Stars,"  Collins.    D.  Appleton  &  Co.,  New  York. 

For  those  whose  interest  in  the  study  of  the  heavens  does  not 
wane,  a  most  useful  and  interesting  device  is  "The  Barritt-Serviss 
Star  and  Planet  Finder."  This  is  a  cleverly  constructed,  revolving 
chart  which  furnishes  in  a  moment's  time  a  map  of  the  heavens  for 
any  hour  of  any  night  of  the  year.  Address  Leon  Barritt,  Publisher. 
(See  footnote,  p.  569.) 

PROJECT  V.  —  How  to  Clean  Drain  Pipes,  pages  56  and  57 
i 

Nothing  has  a  more  important  bearing  on  the  health  of  a  house- 
hold than  the  condition  of  drain  pipes  leading  from  sinks,  washbowl, 
and  bathtubs.  Typhoid,  diphtheria,  and  other  deadly  germs  find 
ideal  breeding  places  in  the  grease  and  filth  of  these  drains.  House- 
keepers who  keep  then-  homes  otherwise  immaculate  sometimes  for- 
get the  cleansing  of  drains  because  the  unsanitary  accumulations 
are  out  of  sight.  No  sink  drain  ought  ever  to  go  without  attention 
until  the  waste  water  runs  slowly  or  the  pipes  are  clogged. 

If  a  sink  becomes  clogged,  a  cupful  of  lye  in  a  wash-boilerful  of 
boiling  water  will  generally  cut  the  grease  that  has  gathered  and 
holds  other  waste  accumulations.  Chloride  of  lime  used  in  the 
same  proportions  will  accomplish  the  same  purpose.  The  solution 
should  be  poured  in  fast  enough  so  that  it  will  run  through  with 
considerable  force.  If  this  fails,  cover  the  opening  to  the  drain  and 
fill  the  sink  with  a  second  boilerful  of  the  solution.  Then  with  a 
force-cup  (familiarly  known  as  a  "plumber's  friend")  force  the 
mixture  down  the  drain  pipe.  This  seldom  fails  to  produce  the 
desired  result. 


PROJECTS  571 

To  keep  a  sink  drain  in  sanitary  condition,  flush  it  daily,  prefer- 
ably in  the  evening,  with  a  dishpanful  of  clear  boiling  water  in  which 
a  tablespoonful  of  washing  soda  has  been  dissolved.  Once  a  week, 
flush  with  a  wash-boilerful  of  boiling  water  in  which  a  teacupful  of 
chloride  of  lime  has  been  dissolved.  Lye  must  be  handled  with 
such  great  care  that  it  is  best  not  to  use  it  unless  its  use  is  made 
necessary  by  clogged  pipes.  At  any  rate,  chloride  of  lime  is 
fully  as  effective  for  disinfecting  and  almost  as  effective  for 
cleansing. 


PROJECT  VI.  —  How  to  Prepare  Certain  Acids  and  Bases  for  Re- 
moving Stains,  page  57 

The  most  common  acids  for  removing  stains  are  lemon  juice, 
lactic  acid  (the  acid  found  in  sour  milk  and  buttermilk),  tartaric 
acid,  oxalic  acid,  and  salts  of  lemon  in  solution.  If  spots  can  be  re- 
moved without  the  use  of  oxalic  acid  or  salts  of  lemon,  so  much  the 
better.  They  are  more  apt  to  cause  injury  to  fabrics  than  milder 
acids,  and  besides  they  are  rank  poisons. 

The  most  common  bases  for  taking  out  stains  are  ammonia,  bak- 
ing soda,  washing  soda,  borax,  and  Javelle  water. 

The  least  familiar  of  these  acids  and  bases  are  probably  tartaric 
acid,  oxalic  acid,  salts  of  lemon,  and  Javelle  water. 

Tartaric  Acid.  —  This  may  be  prepared  by  dissolving  any  given 
quantity  of  cream  of  tartar  in  an  equal  or  even  smaller  bulk  of  water. 
The  same  effect  may  be  had  by  wetting  the  stain  thoroughly  with 
water  and  applying  the  dry  cream  of  tartar.  This  is  the  more 
common  way  of  using  it,  because  tartaric  acid  prepared  as  above 
indicated  will  not  "keep." 

Oxalic  Acid.  —  Dissolve. commercial  oxalic  acid  crystals  in  ten 
times  their  bulk  of  water.  If  this  solution  proves  too  weak,  add 
crystals  until  desired  strength  is  obtained.  Painters  use  a  very 
strong  solution  of  this  (about  one  part  of  oxalic  acid  crystals  to  two 
parts  of  water)  for  bleaching  stains  out  of  wood.  The  crystals  dis- 
solve much  more  quickly  in  boiling  water,  and  the  solution  should 
be  used  hot  for  bleaching  wood. 


572  EVERYDAY  SCIENCE 

Salts  of  Lemon.  —  This  is  the  common  name  for  oxalate  of  potash. 
It  may  be  purchased  at  a  drug  store  under  either  name.  It  may  be 
used  in  solution,  but  is  generally  applied  to  a  stain  after  the  fabric 
has  been  soaked  in  water  —  as  in  the  case  of  cream  of  tartar. 

Javelle  Water.  —  Dissolve  one  fourth  of  a  pound  of  chloride  of 
lime  in  a  quart  of  boiling  water,  and  a  pound  of  washing  soda  in  a 
second  quart  of  boiling  water.  Pour  the  two  solutions  together  and 
set  the  mixture  aside  to  settle.  Pour  off  the  clear  liquid  and  store 
it  in  bottles  or  a  stone  jug.  This  is  Javelle  water,  a  very  effective 
bleaching  solution  for  white  cotton  or  linen. 

Helpful  Hints  on  the  Treatment  of  Stains 

Direction  for  removing  stains  must  always  depend  both  on  the 
nature  of  the  fabric  and  on  the  kind  of  stain.  Vegetable  fibers, 
such  as  linen  and  cotton,  will  stand  more  vigorous  treatment  than 
wool,  silk,  or  other  animal  fibers.  The  most  common  stains  are 
those  of  acids,  alkalies,  ink,  grass,  iron  rust,  fruit,  mildew,  tar,  paint, 
grease,  and  oil.  The  last  four  enumerated  are  more  easily  removed 
by  substances  that  will  dissolve  them  or  absorb  them.  They  will 
be  discussed  later.  Here  we  are  interested  chiefly  in  stains  that 
may  have  to  be  removed  by  undergoing  chemical  changes. 

Many  stains  may  be  removed  by  solution  (Project  XXVIII)  or 
absorption  (Project  XXXIV)  before  long  exposure  to  the  air  brings 
about  certain  chemical  changes  that  set  the  stain.  Since  strong 
acids  and  bases  must  be  employed  to  remove  such  stains  after  they 
are  set,  it  is  especially  desirable  that  stains  on  delicate  or  colored 
fabrics  be  treated  while  fresh.  Thus  the  use  of  strong  chemicals, 
with  consequent  risk  of  injury  to  the  cloth,  may  be  avoided. 

Where  chemicals  must  be  used,  the  milder  agents  should  be  tried 
first,  and  the  stronger  acids  or  bases  used  only  as  a  final  resort. 
When  the  stronger  acids  are  used,  they  should  be  followed  by 
ammonia  in  order  to  neutralize  the  acid.  It  is  often  wise,  especially 
in  the  case  of  a  valuable  fabric,  to  make  tests  with  a  scrap  of  the 
same  or  a  similar  piece  of  goods  before  running  any  risk  with  the 
treasured  article. 


PROJECTS  573 

Oxalic  acid  and  salts  of  lemon  may  be  used  with  care  on  any  kind 
of  vegetable  or  animal  fabric  that  is  white.  They  will  bleach  colored 
fabrics,  but  the  color  may  often  be  restored  by  the  use  of  ammonia 
followed  by  chloroform.  The  mos't  useful  acid  for  removing  stains 
is  probably  tartaric  acid.  It  cannot  be  made  strong  enough  to  in- 
jure fabrics,  and  if  the  cream  of  tartar  is  mixed  with  an  equal  bulk 
of  salt,  it  is  not  likely  to  cause  colors  to  run.  It  is  only  slightly 
poisonous. 


PROJECT  VII.  —  How  to  Remove  Acid  Stains 

Many  acids  will  stain  fabrics  of  any  sort.  Some  acids  which 
will  not  affect  white  goods  will  stain  colored  goods,  especially  blues 
and  blacks. 

To  Bleach  Acid  Stains  from  White  Cotton  or  Linen.  —  (a)  Wash 
the  article,  dip  the  stain  in  Javelle  water,  and  rinse  in  clear  cold 
water.  Or,  (6)  dampen  the  stain  and  expose  it  to  the  fumes  of 
burning  sulphur. 

To  Neutralize  Acid  Stains  in  Goods  of  Any  Fabric  or  Color.  — 
Apply  ammonia  to  the  stain.  In  the  case  of  colored  silk  or  other 
delicate  colored  fabrics,  apply  the  ammonia  very  gently.  A  camel's 
hair  brush  or  a  medicine  dropper  is  recommended  for  the  purpose. 
Take  care  not  to  rub  the  ammonia  into  the  stain  or  it  may  cause  the 
color  to  run.  If  the  color  is  affected,  apply  chloroform  to  restore  it. 

PROJECT  VIII.  —  How  to  Remove  Alkali  Stains 

White  or  Colored  Goods.  —  If  fabrics  of  any  sort  are  stained  by 
washing  soda,  lime,  or  other  strong  alkalies,  moisten  the  stain  with 
lemon  juice,  vinegar,  or  tartaric  acid.  Afterwards  apply  chloro- 
form, if  necessary  to  restore  the  color. 

PROJECT  IX.  —  How  to  Remove  Ink  Stains 

Fresh  Ink  Stains.  —  (a)  If  possible,  ink  stains  should  be  treated 
immediately,  before  they  have  a  chance  to  be  set.  Wet  the  fresh 


574  EVERYDAY   SCIENCE 

ink  spot  immediately  with  water,  or  preferably  with  warm  milk, 
and  cover  it  with  dry  starch,  French  chalk,  or  salt,  or  weight  a  clean 
blotter  on  the  stain.  Remove  the  absorbent  or  change  the  blotters 
as  the  ink  is  absorbed.  Keep  the  spot  wet  and  repeat  the  operation 
until  the  ink  is  removed.  This  treatment  is  safe  for  any  fabric. 
If  the  milk  leaves  a  greasy  stain,  remove  it  with  benzine  or  carbona. 

(&)  For  any  fabric  that  will  stand  soap  and  water,  melt  pure  tal- 
low and  pour  it  over  the  fresh  ink  stain.  If  the  article  is  small,  dip 
it  in  the  tallow.  Remove  the  tallow  after  an  hour  or  so  with  hot 
water  and  soap.  Many  dyers  and  cleaners  do  this  first,  because  it 
cannot  hurt  the  fabric  and  it  may  obviate  the  risk  of  using  chemicals. 

Old  Ink  Stains.  —  Test.  —  Before  using  any  chemical  on  an  ink 
stain  that  has  set,  make  the  following  test,  if  possible,  of  the  ink 
that  caused  the  stain :  Write  a  few  lines  on  a  piece  of  paper  and  allow 
the  ink  to  dry.  Better  than  this,  take  a  specimen  of  writing  with 
the  ink  that  is  several  days  or  weeks  old.  If  when  the  paper  is 
dipped  in  water  the  ink  blurs  or  smirches  badly,  it  probably  con- 
tains a  coal-tar  product  known  as  nigrosine.  The  effect  of  certain 
acids  on  this  coloring  matter  is  to  make  it  almost  indelible.  In 
such  a  case  use  a  strong  solution  of  washing  soda  or  apply'  Javelle 
water  to  the  stain  with  a  brush  or  sponge  and  rinse  in  clear  cold 
water  from  tune  to  time.  Do  not  use  an  acid. 

To  Remove  Ink  That  Does  Not  Contain  Nigrosine.  —  Old-fashioned 
inks  depended  oh  a  compound  of  iron  for  the  black  coloring.  Most 
modern  blue-black  inks  have,  in  addition  to  an  iron  compound  in 
their  make-up,  certain  aniline  dyes.  Acids  mentioned  below  change 
the  iron  compound  so  that  it  will  dissolve  in  water,  but  the  acid 
must  be  followed  by  a  bleaching  compound  to  remove  the  color  of 
the  aniline  dyes.  Following  are  the  treatments  suggested.  The 
first  two  are  very  mild  treatments  ;  the  third  mild,  but  much  more 
effective ;  while  the  fourth  is  to  be  reserved  for  very  stubborn  stains. 

(a)  Wet  the  stain  with  lemon  juice  and  cover  with  salt.  To 
hasten  the  action  of  the  acid  and  salt,  expose  to  the  sun,  hold  in  the 
steam  of  a  tea-kettle,  or  lay  the  cloth  over  a  plate  that  is  used  as  a 
cover  for  a  sauce  pan  containing  boiling  water.  Afterward  expose 
the  spot  to  the  fumes  of  sulphur  (sulphur  dioxide)  or  apply  Javelle 


PROJECTS  575 

water  with  a  brush  or  sponge.     Rinse  thoroughly  in  clear  cold 
water.    Repeat  if  necessary. 

(6)  Soak  in  sour  milk  and  salt  or  in  buttermilk  and  salt.  Cover 
the  stain  with  salt  and  expose  to  the  sun. 

(c)  Wet  the  stain  thoroughly  and  cover  with  cream  of  tartar. 
Proceed  then  as  in  (a) .     Most  ink  stains  will  yield  to  this  treatment. 

For  Delicate  or  Colored  Fabrics.  —  Wet  the  stain  thoroughly  and 
cover  with  cream  of  tartar  mixed  with  an  equal  bulk  of  salt.  Sponge 
very  lightly  with  clear  water  and  expose  to  sulphur  fumes.  If  the 
color  is  affected,  apply  ammonia  with  a  camel's-hair  brush  or  a 
medicine  dropper  and  follow  with  an  application  of  chloroform. 
Repeat  if  necessary. 

(d)  For  Stubborn  Spots  on  Heavy  White  Goods.  —  Wet  the  stain 
thoroughly  and  rub  in  salts  of  lemon  or  oxalic  acid  with  a  small 
stiff  brush,  keeping  the  stain  over  a  hot  plate  as  in  (a).     Sponge 
with  ammonia  and  bleach  with  sulphur  fumes  or  Javelle  water  as 
in  (a).     Rinse  in  clear  water.    Salts  of  lemon  and  oxalic  acid  are 
very  poisonous  if  taken  internally. 

PROJECT  X.  —  How  to  Remove  Grass  Stains 

(a)  Sponge  out  the  stain  while  it  is  fresh  with  clear  water.  If 
this  is  not  sufficient,  sponge  the  stain  with  alcohol  before  it  is  set. 
Do  not  use  alcohol  if  the  stain  is  several  hours  old. 

(6)  Another  effective  method  for  fresh  stains  is  to  cover  the  stain 
with  lard,  allow  it  to  stand  thus  for  24  hours,  and  then  wash  with 
hot  water  and  soap. 

(c)  If  the  stain  is  old,  the  green  coloring  matter  of  the  grass  has 
undergone   chemical  changes  by  being  exposed  'to  air.    Alcohol 
will  then  change  the  green  spot  to  a  dark  brown  spot  that  will  not 
wash  out.    Wet  an  old  stain  and  apply  cream  of  tartar  and  salt  in 
equal  bulk.     If  this  leaves  a  light  brown  stain,  sponge  it  with  water. 
If  colored  fabric  is  affected  by  this  treatment,  sponge  with  ammonia 
and  follow  with  an  application  of  chloroform. 

(d)  An  old  grass  stain  on  white  goods  may  be  removed  b; 

ing  with  a  mixture  of  equal  parts  of  clear  water  and  Javelle  water. 


576  EVERYDAY  SCIENCE 

PROJECT  XI.  —  How  to  Remove  Rust  Stains 
The  simplest  method  is  to  wet  the  stain  with  lemon  juice,  cover 
with  salt,  and  expose  to  the  sun. 

If  this  fails,  wet  the  stain  and  cover  it  with  a  mixture  of  equal 
parts  of  cream  of  tartar  and  salt.  Expose  the  spot  to  the  sun,  hold 
it  in  the  steam  of  a  tea-kettle,  or  over  a  hot  plate  as  suggested  in 
Project  IX.  This  may  be  used  on  any  kind  of  fabric  and  is  not 
likely  to  injure  even  colored  fabrics.  If  it  does  affect  colors,  sponge 
lightly  with  ammonia  and  follow  with  an  application  of  chloroform. 
On  any  white  fabric,  dilute  oxalic  acid,  salts  of  lemon,  or  Javelle 
water  may  be  used.  Follow  either  of  the  first  two  with  ammonia 
and  rinse  in  clear  water. 

PROJECT  XII.  —  How  to  Remove  Fruit  Stains 

Fresh  Fruit  Stains.  —  All  fruit,  tea,  and  coffee  stains  should  be 
treated  while  they  are  fresh.  Plum,  peach,  and  blackberry  stains 
are  especially  stubborn  if  they  become  set.  While  the  stain  is 
fresh,  stretch  the  cloth  over  a  bowl,  cover  the  stain  with  baking 
soda  or  washing  soda,  and  pour  boiling  water  through  the  cloth  until 
the  soda  is  dissolved.  If  necessary,  let  the  cloth  sag  into  the  water 
in  the  bowl  for  a  while. 

Another  method  is  to  soak  the  fresh  stain  in  warm  milk  and  salt, 
cover  with  salt,  and  expose  to  the  sun. 

Old  Fruit  Stains.  —  To  a  fruit  stain  on  any  white  fabric,  apply 
Javelle  water,  salts  of  lemon  in  solution  or  dilute  oxalic  acid  and 
follow  with  ammonia. 

For  wool,  silk,  delicate  and  colored  fabrics,  wet  the  stain  with 
a  mixture  of  equal  parts  of  alcohol  and  ammonia.  Sponge  gently 
with  alcohol  until  stain  is  removed.  Sponge  gently  with  chloroform 
to  restore  color  if  necessary. 

PROJECT  XIII.  —  How  to  Remove  Mildew 

(a)  If  the  fabric  will  stand  it,  boil  in  strong  borax  water. 
(6)  Soak  the  stain  in  buttermilk  or  sour  milk  and  salt,  cover  with 
salt,  and  expose  to  the  sun. 


PROJECTS  577 

(c)  Soak  the  stain  in  lemon  juice.    Apply  common  salt  and  pow- 
dered starch  or  salt  and  expose  to  the  sun. 

(d)  Keep  the  stain  wet  with  Javelle  water  and  expose  to  the  sun. 

(e)  Wash  the  stain  with  Ivory  soap  or  any  pure  white  soap.     Rub 
in  powdered  chalk  with  a  flannel  cloth.    Cover  with  more  chalk 
and  lay  in  the  sun. 

(/)  Dissolve  two  teaspoonfuls  of  shavings  of  any  hard  white  soap 
in  four  teaspoonfuls  of  water,  add  a  teaspoonful  of  starch,  one  half 
teaspoonful  of  salt,  and  the  juice  of  half  a  lemon.  Mix  thoroughly 
and  apply  to  the  mildewed  stain  with  a  brush.  Keep  the  spot  wet 
with  this  mixture  until  the  stain  disappears. 

Of  these  six  methods,  6,  c,  and  /  are  probably  the  most  commonly 
used. 


PROJECT  XIV.  —  How  to  Test  Fabrics  with  Acids  and  Bases, 
pages  55-57 

There  are  numerous  ways  of  testing  fabrics  to  determine  what 
they  are  made  of.  Experts  can  easily  distinguish  the  fibers  of  silk, 
wool,  cotton,  linen,  and  other  fabrics  under  the  microscope.  The 
various  fibers  have  their  characteristic  appearances  and  odors  while 
burning  that  may  be  observed  and  distinguished  by  experimenta- 
tion. Very  reliable  tests  may  also  be  made  with  the  aid  of  certain 
acids  and  bases. 

To  Distinguish  between  Wool  and  Cotton.  —  If  you  are  in  doubt 
as  to  whether  a  piece  of  goods  is  wool  or  cotton,  boil  a  sample  of  it 
for  five  minutes  in  a  strong  solution  of  caustic  soda  (sodium  hy- 
droxide). If  it  is  all  wool,  it  will  dissolve  completely.  If  it  is  all 
cotton,  it  will  not  be  visibly  affected,  except  possibly  to  appear 
somewhat  shrunken  and  a  bit  more  silky.  If  the  fabric  is  mixed 
wool  and  cotton,  the  wool  will  be  dissolved,  leaving  the  cotton  that 
was  woven  with  it.  If  it  is  mixed  wool  and  silk,  the  wool  will  dis- 
solve first,  leaving  the  silk.  About  15  or  20  minutes  more  of 
boiling  will  dissolve  the  silk. 

Caustic  soda  and  other  strong  alkalies  dissolve  wool  wry  readily, 
but  do  not  so  affect  cotton.  In  fact,  cotton  is  treated  with 


578  EVERYDAY   SCIENCE 

soda  as  the  first  step  in  mercerizing  it.  Silk  also  dissolves  in  caus- 
tic soda,  but  not  so  readily  as  wool. 

To  Distinguish  between  Silk  and  Mercerized  Cotton.  —  Put  a 
little  concentrated  hydrochloric  acid  in  a  test  tube  and  heat  it 
gently,  stirring  it  with  a  chemical  thermometer  until  the  ther- 
mometer registers  50°  C.  or  a  little  less.  Immerse  a  sample  of  the 
fabric  hi  the  acid  and  keep  it  there  for  three  or  four  minutes,  being 
careful  to  keep  the  acid  at  a  fairly  even  temperature.  If  the  fabric 
is  silk,  the  sample  will  be  dissolved.  If  it  is  mercerized  cotton,  it 
will  remain  intact.  Concentrated  hydrochloric  acid  will  not  dis- 
solve either  wool  or  cotton. 

To  Distinguish  between  Cotton  and  Linen.  —  The  simplest  test 
to  determine  whether  a  fabric  is  linen  or  cotton  is  made,  not  with 
an  acid  or  an  alkali,  but  with  olive  oil.  Thoroughly  soak  the  fabric, 
or  a  sample  of  it,  hi  olive  oil  for  about  five  minutes.  Remove  the 
excess  of  oil  by  pressing  the  cloth  between  blotters.  If  the  fabric 
is  linen,  it  will  now  be  translucent.  If  it  is  cotton,  it  will  be  as 
opaque  as  it  was  before  soaking  in  the  oil. 

A  most  interesting  book  for  anyone  who  is  interested  in  chem- 
istry in  everyday  life  is  "The  Amateur  Chemist,"  A.  F.  Collins. 
D.  Appleton  &  Co. 

PROJECT  XV.  —  How  to  Make  Soap  from  Waste  Fats  at  Home, 
page  57 

Collecting  enough  waste  fats  for  a  batch  of  soap  is  likely  to  prove 
a  tedious  performance.  If  through  carelessness  or  impatience 
a  pupil  then  fails  to  produce  soap,  there  is  a  discouraging  loss  of 
time,  effort,  and  money.  It  is  recommended,  therefore,  that  the 
first  batch  of  soap  be  made  a  community  affair  for  the  entire  class; 
or  that  the  class  be  divided  into  groups,  each  group  undertaking 
the  project. 

If  there  is  a  school  lunch-room  or  cafeteria,  pupils  may  be  able 
to  enlist  the  aid  of  the  school  kitchen  in  -collecting  waste  fats  for 
the  experiment.  If  not,  pupils  may  each  contribute  a  few  ounces 
of  fat  from  their  home  kitchens  and  may  divide  the  expense  of 


PROJECTS  579 

borax  and  potash.  Experiments  in  soap-making  on  a  very  small 
scale  are  somewhat  difficult  to  perform.  It  will  be  found  easier 
to  produce  soap  from  five  pounds  of  fat  than  from  five  ounces.1 
Follow  the  directions  carefully  and  patiently : 

Into  a  six-quart  iron  or  heavily  enameled  vessel  put  2  quarts  of 
water  and  heat  it  to  boiling.  Remove  from  the  stove  and  dissolve 
1  can  of  Babbitt's  potash  in  the  hot  water. 

In  a  third  quart  of  hot  water,  dissolve  one  half  pound  of  borax. 

Pour  the  borax  solution  into  the  potash  solution  and  set  the 
mixture  aside  to  cool. 

Melt  5  pounds  of  fat  and  strain  it  through  three  layers  of  cheese- 
cloth. Allow  this  fat  to  cool  to  a  soft  paste-like  consistency. 

The  next  step  requires  patience.  Add  the  fat,  a  spoonful  at 
a  time,  to  the  potash-borax  solution,  and  stir  each  spoonful  into  the 
solution  slowly  and  carefully.  After  the  fat  is  all  in,  stir  the  mix- 
ture slowly  for  fifteen  minutes. 

If  at  the  end  of  this  time  the  soap  is  not  of  a  paste-like  consistency, 
let  it  stand,  giving  it  an  occasional  slow  stirring.  Your  success 
may  be  immediate,  or  your  patience  may  be  taxed  for  a  day  or 
more.  Do  not  give  up. 

When  the  mixture  has  become  pasty,  pour  it  into  a  rectangular 
pan  lined  with  oil  paper.  As  soon  as  it  hardens,  it  may  be  cut  into 
bars.  It  should  be  allowed  to  dry  out  for  several  weeks  before  it  is 
used.  This  soap  is  of  very  good  quality  and  may  be  used  for  toilet 
purposes. 

Coloring,  Perfuming,  and  Molding.  —  It  is  recommended  that  the 
pupil  confine  his  first  efforts  to  producing  soap.  After  he  has  made 
a  batch  or  two,  he  may  wish  to  try  experiments  with  coloring  and 
perfuming.  Coloring  matter,  such  as  eosin  (a  very  small  amount ), 
should  be  added  after  about  ten  minutes  of  stirring  and  before  the 
mixture  begins  to  become  jelly-like.  A  few  drops  of  oil  of  lemon 
or  some  other  perfume  may  also  be  added  at  the  same  time. 

After  the  soap  has  hardened,  it  may  be  remelted  with  a  gentle 
heat  and  poured  into  molds  lined  with  oiled  paper. 

1  Collecting  waste  fats  at  home  though  tedious  work  is  to  be  en- 
couraged, as  the  soap  made  therefrom  will  repay  the  effort 


580  EVERYDAY   SCIENCE 

PROJECT  XVI.  —  How  to  Remove  Dents  in  Wood, 
pages  64-67 

A  heavy  blow  of  a  hammer  will  leave  a  dent  in  wood.  What 
happens  is  that  the  molecules  of  the  wood  at  this  particular  place 
have  been  forced  into  smaller  space;  that  is,  the  spaces  between 
them  have  been  lessened  (see  p.  67  of  this  book).  If  the  wood 
had  been  as  elastic  as  rubber,  the  molecules  would  have  regained 
their  original  positions  immediately;  but  wood  has  not  great 
elasticity. 

If  now  we  can  cause  the  wood  to  absorb  enough  heat  and  moisture, 
the  molecules  will  be  driven  back  to  their  original  relative  positions. 
Heat  an  iron  very  hot.  Soak  several  thicknesses  of  soft  brown  paper 
in  hot  water.  Lay  this  pad  of  wet  paper  over  the  dent  and  cover 
it  with  a  double  thickness  of  cloth  soaked  in  hot  water.  Apply  the 
hot  iron  to  the  cloth  just  above  the  dent,  and  let  it  stand  until  the 
cloth  and  paper  are  nearly  dry.  If  the  dent  is  deep,  this  process 
may  have  to  be  repeated  several  times. 

PROJECT  XVII.  —  How  a  Boy  Scout  Makes  Fire  without  Matches, 
page  72 

Five  things  are  necessary  to  produce  a  rubbing-stick  fire  :  a  drill 
or  spindle,  a  fire-block  or  hearth,  a  hand-socket,  a  bow,  and  tinder. 


FIGURE  5 

In  choosing  wood  for  making  the  drill  and  fire-block,  great  care 
must  be  exercised.  The  wood  should  be  dry  and  long-seasoned, 
but  sound.  Gummy  and  resinous  woods  should  be  avoided.  A  test 
for  good  wood  for  this  purpose  is  that  the  wood-dust  ground  off 
shall  be  smooth  to  the  touch,  not  gritty  or  sticky.  Two  of  the 
best  and  most  widely  distributed  woods  are  cottonwood  and  willow. 
Better  even  than  these  are  the  cedar,  the  cypress,  or  the  tamarack, 
if  they  can  be  had.  If  none  of  these  is  at  hand,  try  soft  maple,  elm, 
poplar,  sycamore,  or  buckeye. 


PROJECTS  581 

Drill.  —  Out  of  a  straight  dry  branch  or  piece  of  seasoned  wood, 
whittle  a  roughly  rounded  spindle,  about  12  inches  long,  and  not 
more  than  £  inch  in  diameter.  Sharpen  the  two  ends  of  the  stick, 
as  shown  in  Figure  5. 

Fire-block.  —  Take  a  piece  of  wood  not  more  than  12  inches 
long,  2  or  3  inches  wide,  and  not  more  than  J  inch  thick.  On  one 


FIGURE  6 

side  of  this  board,  well  toward  one  end,  cut  a  notch  J  inch  deep, 
and  bevel  it  slightly  toward  the  under  side  of  the  board.  About 
|  inch,  or  less,  from  the  tip  of  the  notch  make  a  little  hollow  or  pit 
in  the  board,  as  shown  in  Figure  6,  A. 

Hand-socket.  —  If  nothing  better  is  at  hand,  take  a  pine  or 
hemlock  knot  that  will  just  fit  comfortably  into  the  palm  of  the 
hand.  Make  a  pit  in  the  center  of  one  of  the 
flat  surfaces  of  the  knot,  about  J  inch  in  diam- 
eter and  |  inch  deep. 

If  you  are  going  to  practice  fire-making  on 
camping  trips,  you  will  find  it  a  great  saving 
of  time  to  have  a  socket  made  for  your  per- 
manent use.    Take  a  solid   block  of  wood  5  or  6  inches  long, 
If  inches  wide,  and  1£  inches  thick.    Set  in  the  middle  of  one  fa< ••• 
of  this  block  a  piece  of  soapstone  or  marble  1  inch  square  and  about 
£  inch  deep.     In  the  center  of  this  piece  of  stone  make  a  small 
smooth  pit,  |  inch  wide  and  |  inch  deep.    Smooth  and  round  tin- 
opposite  face  of  the  block  so  that  it  will  fit  your  palm  mmfortnlily 
and  can  be  grasped  firmly.    The  socket  is  now  ready  for  u>. 
ure  7). 

Bow.  —  (a)  For  this,  any  slightly  curved  rigid  branch  or  >tirk, 
18  to  24  inches  long,  may  be  used.     Fasten  a  thong  of  buckskin. 


582 


EVERYDAY   SCIENCE 


belt-lacing,  or  of  any  pliable  leather,  about  f  inch  wide,  to  the  bow, 
as  shown  in  Figure  8.     The  thong  should  be  just  long  enough  so 


FIGURE  8 

that  when  it  is  given  one  turn  around  the  drill  it  will  be  stretched 
taut  (Figure  9). 

Tinder.  —  Any  dry,  finely  divided  material  that  readily  bursts 
into  flame  from  a  spark  is  called  tinder.     Shredded  cedar  bark, 

a  wad  of  dry  grass, 
crumpled  dry  leaves, 
willow  catkins,  scraped 
cedar  or  spruce  wood 
will  serve  admirably. 
Any  observing  person 
will  be  able  to  find 
plenty  of  good  tinder 
in  a  forest. 

In  addition  to   this 
tinder,   which  is   used 
to   nurse   the   glowing 
spark  into   flame,   the 
fire-maker  should  have 
at    hand    a    collection 
of  twigs,  long-stemmed 
dry     grass,     splinters, 
slivers    of    dry    bark, 
etc.,   to    be    used    as 
kindling  for  the  larger 
fuel  that  is  to  follow. 
To  Make  Fire.  —  Set  the  fire-block  on  firm  ground  or  on  flat 
rocks  or  on  any  foundation  where  the  block  can  be  kept  from  slip- 
ping or  joggling.     Slip  a  thin  chip  under  the  notch  of  the  hearth. 


FIGURE  9.  —  TOOLS  IN  POSITION  TO  MAKE  FIRE. 

At  A  is  shown  a  hole  that  has  been  bored  in 
producing  fire. 


PROJECTS  583 

Turn  the  thong  of  the  bow  once  around  the  drill.  If  the  thong 
is  of  the  right  length,  it  will  now  be  taut. 

Set  one  point  of  the  drill  into  the  pit  near  the  point  of  the  notch 
of  the  fire-block,  fit  the  upper  end  into  the  hand-socket,  and  with 
your  left  hand  hold  the  drill  perpendicular  to  the  block.  Anchor 
the  fire-block  with  your  left  foot,  and  steady  your  left  hand  by 
resting  your  left  wrist  against  your  left  shin.  This  is  to  enable 
you  to  keep  the  drill  steadily  in  an  upright  position  (Figure  9). 

Now  with  the  right  hand  draw  the  bow  slowly  and  steadily  back 
and  forth  the  full  length  of  the  thong,  pressing  lightly  on  the  hand- 
socket.  Keep  the  bow  horizontal,  and  do  not  touch  the  drill  with 
it  as  you  saw  back  and  forth.  The  twirling  motion  of  the  drill  soon 
makes  it  bite  into  the  block,  boring  out  powdered  wood.  When 
it  begins  to  smoke,  put  a  little  more  pressure  on  the  socket  and  drill 
faster.  When  the  dust  comes  out  in  a  compact  mass  and  the  smoke 
increases  to  a  considerable  volume,  you  probably  have  the  spark. 

Carefully  lift  the  fire-block  so  as  to  leave  the  smoking  powder 
undisturbed  on  the  chip.  Gently  fan  this  with  your  hand  into  a 
bright  glow.  Then  put  a  wad  of  tinder  gently  over  the  glowing 
powder  and  blow  until  the  tinder  bursts  hi  to  flame.  Follow  this 
with  the  kindling  and  your  fire  is  started. 

N.  B.  If  you  are  left-handed,  you  will  probably  reverse  the 
directions  for  employing  the  right  and  left  hands. 

PROJECT  XVIII.  —  How  to  Make  Fire  with  Flint  and  Steel, 
page  73 

It  is  much  easier  to  make  fire  with  flint  and  steel  than  to  pro- 
duce a  rubbing-stick  fire.  Flint  and  steel  and  even  tinder  fuse  may 
be  bought  of  dealers  in  camping  outfits.  Many  lighting  devices 
for  pocket  use  are  based  on  the  principle  of  striking  fire  from  flint 
with  steel. 

But  neither  the  flint  and  steel  nor  the  tinder  have  to  U-  pur- 
chased. Any  piece  of  steel  and  any  piece  of  quartz  or  hornstone 
or  flint  may  be  made  to  serve  your  purpose.  If  you  want  to  be  sure 
of  having  "punk"  that  will  be  sure  to  catch  the  spark,  soak  pieces 


584  EVERYDAY  SCIENCE 

of  cotton  wicking  in  a  solution  of  saltpeter  and  dry  them  thoroughly. 
Of  the  materials  to  be  found  in  a  forest  nothing  is  better  than  dried 
fungus  growths  of  various  sorts.  Thoroughly  dried  puff-balls,  or 
the  flat  white  fungus  growths  found  on  decaying  tree-trunks,  or 
dried  lichens  or  moss  are  among  the  best  materials.  Dust  or  very 
fine  shavings  scraped  from  dry  cedar  bark,  spruce,  or  pine  will 
catch  the  spark  readily. 

To  obtain  the  spark,  rest  the  flint  on  the  "punk"  and  strike 
downward  with  the  steel  along  the  edge  of  the  flint  so  as  to  throw 
the  shower  of  sparks  into  the  "punk." 

When  you  have  the  spark  in  the  "punk,"  nurse  it  into  a  glow 
exactly  as  hi  the  case  of  the  rubbing-stick  fire,  transform  the  glowing 
spark  into  flame  with  the  aid  of  tinder,  and  add  the  kindling  and 
larger  fuel  gradually  until  your  fire  is  established. 

PROJECT  XIX.  —  How  to  Operate  a  Fire-extinguisher, 
pages  79  and  80 

The  principle  of  the  fire-extinguisher  which  produces  carbon 
dioxide  is  carefully  explained  on  pages  79  and  80  of  the  body  of 
the  book.  Every  pupil  of  junior  high  school  age  ought  to  know 
how  to  operate  one  of  the  extinguishers  without  a  moment's 
hesitation. 

Every  modern  fire-extinguisher  has  explicit  directions  for  operat- 
ing it  printed  on  the  metal  container.  These  directions  should  be 
followed  to  the  letter.  It  is  especially  important  that  the  ex- 
tinguisher should  be  discharged  occasionally  so  as  to  have  the 
machine  always  charged  with  fresh  chemicals. 

Build  a  small  fire  in  the  open,  away  from  all  buildings,  and  use 
a  fire-extinguisher  to  smother  the  fire.  Remember  that  the  pur- 
pose of  these  machines  is  to  cover  the  fire  with  a  blanket  of  carbon 
dioxide  gas.  Play  the  spray  from  the  machine  over  the  whole  fire 
so  as  to  cut  off  the  oxygen  from  all  burning  material. 

When  you  have  extinguished  the  fire,  refill  the  cylinder  according 
to  directions,  not  neglecting  to  wash  it  out  thoroughly  before  re- 
filling. If  you  are  at  all  in  doubt  as  to  whether  you  have  refilled 


PROJECTS  585 

correctly,  discharge  the  extinguisher  again  in  a  second  experiment 
with  a  small  bonfire. 

One  of  the  machines  that  generates  carbonic  acid  gas  also  pro- 
duces a  foam,  the  bubbles  of -which  imprison  the  carbonic  acid  gas 
and  form  a  sort  of  foamy  blanket  that  is  especially  effective  in 
extinguishing  burning  oils. 

Another  very  commonly  used  extinguisher,  which  is  compact 
enough  to  be  convenient  for  automobile  use,  is  filled  with  a  liquid 
that  contains  carbon  tetrachloride.  When  this  liquid  comes  in 
contact  with  heat,  it  is  readily  converted  into  a  heavy  gas  whirh 
smothers  the  fire  just  as  carbon  dioxide  does.  This  machine  is 
operated  like  a  simple  hand-pump. 

PROJECT  XX.  —  How  to  Make  a  Fireless  Cooker  at  Home, 
page  91 

A  very  satisfactory  fireless  cooker  may  be  made  at  home  at 
relatively  slight  expense. 

The  Box  or  Container.  —  The  outside  of  the  box  may  be  a  tightly 
built  wooden  box,  an  old  trunk,  a  galvanized  iron  ash  can,  a  large 
lard  tin  or  butter  firkin. 

A  well-built  conveniently  sized  box  (Figure  10,  A),  with  a  hinged 
cover  (Figure  10,  H),  fitted  with  a  hasp  lock  is  perhaps  the  most 
satisfactory  container,  although  the  cooker  incased  in  metal  has 
the  advantage  of  being  fireproof.  If  a  box  is  to  be  used,  its  size 
will  depend  on  the  size  of  the  metal  nest  which  holds  the  cooking 
vessel  (Figure  10,  (7).  If  possible,  the  box  and  the  nest  should  be 
large  enough  to  accommodate  a  six-quart  cooking  vessel  (Figure 
10,  D).  There  must  be  enough  space  in  the  container  to  allow  for 
at  least  four  inches  of  packing  material  above,  below,  and  all  around 
the  metal  nest. 

Packing  or  Insulating  Material.  —  For  insulating  material  a 
variety  of  substances  may  be  used.  Crumpled  or  shredded  m  \\>- 
paper,  sawdust,  cotton-seed  hulls,  ground  cork  (such  as  is  ux-.l 
in  packing  Malaga  grapes),  wool,  Spanish  moss,  hay,  straw,  and 
excelsior  may  be  used  satisfactorily  (Figure  10,  B). 


586 


EVERYDAY   SCIENCE 


H 


It  is  safer  to  pack  the  container  with  some  non-inflammable 
material,  such  as  asbestos.  A  cheap  and  easily  obtained  substitute 
is  small  cinders  sifted  from  soft  coal  ashes,  which  may  be  obtained 
at  the  boiler  house  of  any  mill  if  soft  coal  is  not  used  in  your  home. 

(Cinders  from  hard 
coal  are  not  quite 
so  good  but  will 
serve.)  Experi- 
ments with  soft 
coal  cinders  made 
by  home  econom- 
ics specialists  for 
the  United  States 
Department  of  Ag- 
riculture showed 
that  this  material 
is  very  nearly  as 
satisfactory  for 
packing  as  crum- 
pled or  shredded 
paper. 

Courtesy  of  U.S.  Department  of  Agricvltwre.         The  Metal   Nest. 
FIGURE  10.  —  LONGITUDINAL  SECTION  THROUGH        —  The     insulating 
FIRELESS  COOKER  material  is  packed 

Showing  details  of  the  construction:  A,  outside  solidly  into  the 
container  (wooden  box,  old  trunk,  etc.) ;  B,  packing  pr.n*Q:npT.  „<,  ^11 
or  insulating  material  (crumpled  paper,  cinders,  etc.)  ;  contamer>  * 
C.  metal  lining  in  nest ;  D,  cooking  kettle ;  E,  soap-  be  described  later, 
stone  plate,  or  other  source  of  heat ;  F,  collar  to  cover  gO  as  to  fit  snugly 
insulating  material;  G,  pad  or  cushion  for  top;  ,  ,  , 

H,  hinged  cover  of  box  or  container.  about     the     metal 

nest  (Figure  10,  C). 

This  nest  should  be  of  a  trifle  greater  diameter  than  the  cooking 
vessel  and  deep  enough  to  hold  a  hot  brick  or  soapstone  (Figure 
10,  E) .  under  the  cooking  vessel.  A  galvanized  iron  bucket  may 
be  used  as  a  metal  nest.  Better  still,  a  tinsmith  can  make  a  galvan- 
ized iron  can  of  the  required  size,  with  straight  sides,  a  rolled  rim, 
and  a  flat  cover  (Figure  11,  A  and  C). 


PROJECTS 


587 


Flange  or  Collar  to  Cover  Insulating  Material.  —  Have  the  tinner 
cut  a  sheet  of  galvanized  iron  exactly  to  fit  the  opening  of  the 
container.  It  should  fit  so  closely  in  length  and  breadth  that 
it  will  just  slip  into  the  container  so  as  to  cover  the  contents  com- 
pletely. In  the  center  of  this  metal  sheet  cut  a  hole  just  large  enough 
to  allow  it  to  be  slipped  over  the  bottom  of  the  metal  nest  and  fitted 
up  snugly  under  the  rolled  rim  as  a  collar  for  the  metal  nest  (Figure 
11,  D).  When  the  nest  is 
put  in  place,  the  collar 
(Figure  10,  F)  covers  the 
packing,  and  serves  the 
important  purpose  of  keep- 
ing it  dry.. 

The  Cooking  '  Vessel  — 
This  should  be  durable  and 
free  from  seams  and  crev- 
ices, which  are  hard  to 
clean.  It  should  have  FIGURE  n. 

perpendicular  sides.  The  -^-  metal  nest,  with  rolled  rim,  B;  C,  cover; 
cover  should  be  as  nearly  D'  detachable  collar  °r  *"*«• 

flat  as  possible  and  should  be  provided  with  a  deep  rim  extending 
well  down  into  the  kettle  to  retain  the  steam.  It  is  possible  to  buy 
kettles  made  especially  for  use  in  fireless  cookers  ;  these  are  provided 
with  covers  which  can  be  clamped  on  tightly. 

Tinned  iron  kettles  should  not  be  used  in  a  fireless  cooker,  for 
although  cheap  they  are  likely  to  rust  from  the  confined  moisture. 
Enameled  ware  kettles,  with  covers  of  the  same  material,  are 
satisfactory.  Aluminum  vessels  do  not  rust,  and  they  may  be 
purchased  in  shapes  that  are  especially  well  adapted  for  use  in  fire- 
less  cookers. 

To  Pack  the  Box  or  Container.  —  Line  the  bottom  of  the  box,  and 
the  sides  to  within  four  inches  of  the  top,  with  10  or  12  sheets  of 
newspaper  or  wrapping  paper,  with  several  thicknesses  of  card- 
board, or  with  sheet  asbestos  £  inch  thick.  Use  a  few  tacks  to 
hold  the  lining  in  place.  Shred  newspaper  into  bits  and  rover 
the  bottom  of  the  box  evenly  and  compactly  with  the  shredded 


588  EVERYDAY   SCIENCE 

I 

paper  to  the  depth  of  four  inches.  Cover  this  with  one  or  two 
thicknesses  of  sheet  asbestos  |  inch  thick.  (If  non-inflammable 
packing  material  is  used,  this  asbestos  cover  for  the  lower  four 
inches  of  packing  is  not  needed.) 

Wrap  the  metal  nest  with  a  sheet  of  the  asbestos  paper,  and  stand 
it,  without  the  collar,  on  top  of  the  packing,  in  the  center  of  the  box. 
Pack  more  shredded  paper,  or  whatever  insulating  material  is  being 
used,  all  around  the  nest  as  solidly  as  possible,  until  it  reaches  the 
rim  of  the  metal  nest.  The  top  of  the  packing  material  and  the  rim 
of  the  nest  should  now  be  about  four  inches,  or  more,  below  the 
cover  of  the  box. 

Carefully  remove  the  metal  nest,  slip  the  galvanized  iron  collar 
over  the  bottom  of  it,  and  slide  it  up  until  it  rests  just  under  the 
rolled  rim  of  the  nest.  Cut  a  piece  of  sheet  asbestos  of  the  same 
shape  as  the  collar  and  fit  it  just  under  the  collar.  Now  replace  the 
nest  carefully,  and  the  collar  with  the  asbestos  lining  under  it  will 
cover  the  packing  completely. 

Cushion  or  Pad.  —  A  cushion  or  pad  (Figure  10,  (?)  must  be  pro- 
vided to  fill  completely  the  space  between  the  collar  or  flange  and 
the  cover  of  the  box.  This  should  be  made  of  some  heavy  goods, 
such  as  denim,  and  stuffed  with  asbestos  fiber,  cotton,  shredded 
paper,  or  excelsior. 

A  heavy  but  very  efficient  pad  may  be  made  by  tying  or  quilting 
newspapers  together  that  have  been  cut  to  fit  the  top  space,  and 
covering  this  paper  pad  with  denim.  The  pad  should  be  exposed 
to  sun  and  air  whenever  it  is  not  in  use. 

To  Use  the  Cooker.  — A  fireless  cooker  is  best  suited  to  those  foods 
which  require  boiling,  steaming,  or  long  slow  cooking  in  a  moist 
heat.  The  classes  of  food  best  adapted  to  the  cooker  are  cereals, 
soups,  meats,  vegetables,  dried  fruits,  steamed  'breads,  and  puddings. 
Less  water  is  needed  than  when  foods  are  cooked  on  the  stove, 
because  there  is  practically  no  escape  of  moisture  from  the  cooking 
kettle. 

To  cook  food,  bring  it  to  a  boil  on  the  stove,  and  at  the  same  time 
heat  the  brick  or  soapstone.  Transfer  the  heated  plate  to  the  nest, 
close  the  cooking  kettle  tightly,  and  place  it  on  the  heated  plate 


PROJECTS  589 

in  the  nest.  Cover  the  nest,  lay  on  the  pad,  close  the  box,  and 
fasten  the  hasp.  Allow  the  food  to  remain  undisturbed  in  the  cooker 
for  six'or  eight  hours. 

Selected  recipes  for  preparing  food  to  be  cooked  in  the  fireless 
cooker  may  be  found  in  Farmers'  Bulletin  No.  771,  "Homemade 
Fireless  Cookers  and  Their  Use." 

Leave  the  cooker  open  when  it  is  not  in  use. 

PROJECT  XXI.  —  How  to  Make  a  Cheap  Ice  Box,  page  92 

The  fireless  cooker  described  in  Project  XX  may  very  readily 
be  used  as  an  ice  box  for  keeping  milk  (or  any  other  food  that  may 
be  put  in  an  inclosed  vessel)  at  a  low  temperature.  Simply  put 
the  bottle  of  milk  tightly  sealed  or  corked  into  the  middle  of  the 
nest  and  pack  ice  solidly  around  it  up  to  the  neck  of  the  bottle. 
Close  the  lid  and  keep  the  box  in  as  cool  and  shady  a  place  as 
possible. 

A  much  better  and  safer  plan,  if  you  wish  to  continue  the  use  of 
the  fireless  cooker  for  an  ice  box,  is  to  obtain  a  covered  bucket  tall 
enough  to  hold  a  milk  bottle  and  of  a  diameter  that  will  allow  about 
an  inch  of  air  space  all  around  between  the  bucket  and  the  metal 
nest.  Pack  the  bottle  in  this  with  crushed  ice,  place  the  bucket  in 
the  nest,  and  close  up  the  box.  The  double  advantage  of  this  is 
that  the  air  space  between  the  bucket  and  the  metal  nest  gives 
extra  insulation  against  the  heat,  and  the  bucket  may  be  more 
easily  taken  out  once  a  day,  emptied  of  water,  washed  with  soap 
and  water,  and  sunned. 

If  the  milk,  or  other  food,  is  cold  when  it  is  put  into  the  cooler, 
it  will  keep  safely  for  24  hours.  If  the  food  is  warm,  or  t  he  weat  her 
is  exceptionally  hot,  the  food  may  require  re-icing  at  the  end  of  12 
hours.  Much  depends  on  the  care  you  have  exercised  in  construct- 
ing your  box.  If  ice  is  not  obtainable,  very  cold  well  wnti T  i-  tin- 
best  substitute.  Put  the  milk  bottle  or  other  closed  container 
into  the  bucket  and  fill  the  bucket  almost  to  the  top  with  cold 
water.  Change  the  water  every  twelve  hours. 

If  you  have  not  made  a  fireless  cooker  in  accordance  with  the 


590 


EVERYDAY   SCIENCE 


specifications  of  Project  XX,  a  still  simpler  contrivance  is 
suggested  by  the  Chicago  Department  of  Health.  Obtain  a  covered 
bucket  tall  enough  and  wide  enough  to  hold  two  quart  bottles  of 
milk.  For  a  nest  get  a  still  larger  bucket  that  will  allow  about  an 
inch  of  insulating  air  space  all  around  between  the  nest  and  the 
inside  bucket. 

To  hold  this,  a  covered  box  at  least  14  inches  square  and  15  inches 
tall  will  be  needed.     Hinge  the  cover,  put  a  hasp  on  it,  and  cleat 


S. 


FIGURE  12. 

M,  milk  in  sealed  bottles,  packed  in  ice  in  covered  bucket ;  S,  sawdust 
packing  around  nest ;  C,  hinged  cover  with  newspapers  cleated  to  it. 

to  the  inside  of  the  cover  about  fifty  thicknesses  of  newspaper,  so 
trimmed  that  the  cover  will  close  tightly.  Cover  the. bottom  of 
the  box  with  three  inches  of  sawdust,  lay  the  nest  in  the  center  of 
the  sawdust  area  and  pack  sawdust  to  the  top  of  the  nest.  A 
vertical  cross  section  of  this  box  is  shown  in  Figure  12.  Use  the 
box  as  directed  in  the  preceding  paragraphs. 

The  principle  that  explains  both  the  fire  less  cooker  and  the  ice 
box  here  described  is  that  a  non-conductor  of  heat  is  interposed 
between  substances  of  different  temperatures,  thus  preventing 
them  from  equalizing  those  temperatures. 

N.B.  If  a  tinned  iron  bucket  is  used,  put  a  little  soda  into  it  each 
day  when  the  ice  is  packed.  This  will  tend  to  prevent  rusting. 


PROJECTS 


591 


PROJECT  XXII.  —  How  to  Make  an  Icekss  Refrigerator,  page  104 

A  very  useful  device  for  the  home  where  ice  is  not  easily  obtain- 
able is  the  iceless  refrigerator  (Figures  13  and  14).  In  farm  homes 
where  large  amounts  of  milk  and  butter  are  to  be  kept,  it  pays  to 
have  a  separate  cooler  for  these 
delicate  foods,  in  order  to  keep 
them  from  absorbing  odors. 
The  following  directions  for 
making  such  a  cooler  contain 
suggestions  taken  from  bulle- 
tins of  the  United  States  De- 
partment of  Agriculture. 

Make  a  stanch  wooden  frame 
for  a  case  42  inches  tall,  with 
the  other  dimensions  14X16 
inches  (Figure  13).  Make  a 
solid  floor  and  top  for  the  case, 
with  matched  boards  if  possible. 
The  solid  top  should  be  set 
below  the  top  of  the  frame- 
work, so  as  to  furnish  an  insert 
to  hold  the  tapering  base  of  a 
14X16  inch  biscuit  pan  (Figure 
13).  Fit  a  full-length  door- 
frame to  the  case  as  in  Figure  1 3, 
and  mount  it  on  brass  hinges. 
Be  sure  that  the  door  fits  closely 
enough  to  be  fly-proof. 

Shelves  may  be  made  of  poul- 
try netting  on  light  wooden  frames,  as  shown  in  Figure  13.    These 
shelves  rest  on  side  braces  set  in  the  frame  at  desired  intervals. 

Now  cover  the  entire  framework  and  door  carefully  with  rust  lens 
wire  screening  of  the  smallest  mesh  obtainable. 

Provide  a  17X18  shallow  bread  pan  in  which  to  stand  the  nit  in- 
case after  it  is  finished. 


Covrtuy  of  U.S.  Department  of  Atriaitturt. 
FIGURE    13.  —  FRAMEWORK    or    THE 
ICELESS  REFRIGERATOR. 


592 


EVERYDAY  SCIENCE 


Give  the  framework,  screening,  shelves,  and  top  and  bottom 
pans  two  coats  of  flat  white  paint.  Give  plenty  of  time  for  drying 
between  coats.  When  the  flat  paint  is  thoroughly  dry,  apply  two 
coats  of  white  enamel.  Remember  that  the  success  of  enameling 
a  surface  depends  largely  on  allow- 
ing sufficient  time  for  drying 
between  coats. 

Before  applying  the  second  coat 
of  enamel,  be  sure  that  the  first 
coat  has  lost  all  trace  of  stickiness. 
The  amount  of  time  necessary 
between  coats  depends  on  the  con- 
dition of  the  atmosphere.  It  may 
be  several  days  before  you  can 
apply  the  last  coat.  Remember 
that  you  want  a  hard  enamel  sur- 
face, and  the  only  way  to  produce 
it  is  to  exercise  enough  patience 
to  allow  thorough  drying  between 
coats  of  paint  and  enamel,  and  a 
final  thorough  drying  before  the 
cloth  cover  is  attached  to  the 
frame. 

A  covering  of  canton  flannel, 
burlap,  or  duck  should  be  cut  and 
hemmed  to  fit  the  case,  as  in  Fig- 
ure 14.  If  canton  flannel  is  used, 
have  the  smooth  side  out.  About  three  yards  of  material  are  needed. 
This  covering  should  extend  down  to  the  very  bottom  of  the  case. 
Button  the  cover  around  the  top  and  bottom  of  the  frame  with 
buggy  hooks  and  eyes.  Another  way  to  button  the  cloth  to  the 
frame  is  to  sew  large  buttons  firmly  to  heavy  strips  of  cloth  at 
desired  intervals,  and  then  tack  these  strips  to  the  edges  where  the 
cover  is  to  be  buttoned.  On  the  edges  of  the  covering  provide 
buttonholes  at  intervals  corresponding  to  intervals  between  buttons 
on  the  strips. 


Courtesy  of  U.S.  Department  of  Agriculture. 

FIGURE  14.  — THE  COMPLETED 

ICELESS  REFRIGERATOR. 


PROJECTS  593 

Arrange  the  covering  so  that  the  door  may  be  opened  without 
unbuttoning  the  edges  of  the  covering.  In  order  to  do  this,  the 
cover  on  the  front  of  the  case  must  be  buttoned  to  the  top  and 
bottom  and  latch  panel  of  the  door,  as  shown  in  Figure  14.  Another 
row  of  buttons  fastens  the  other  vertical  edge  of  the  covering  to 
the  framework  at  the  opening  of  the  door.  Make  sure  that  the 
hems  on  these  vertical  edges  are  extended  far  enough  to  cover  the 
crack  between  the  frame  and  the  closed  door. 

Sew  to  the  top  edge  of  each  side  of  the  covering  a  double  strip 
of  the  same  kind  of  cloth.  Make  these  strips  long  enough  to  extend 
about  3  inches  into  the  biscuit  pan  on  top  of  the  case,  and  taper 
these  strips  to  a  width  of  8  inches. 

Keep  the  upper  pan  filled  with  water.  The  strips  of  cloth  serve 
as  wicks  to  supply  the  sides  of  the  covering  with  moisture  (Experi- 
ment 97,  p.  325).  The  lower  pan  is  to  catch  the  drippings  from 
the  covering.  A  small  amount  of  water  in  the  lower  pan  also  serves 
the  excellent  purpose  of  keeping  ants  and  other  insects  from  the 
refrigerator.  The  only  inconvenience  about  the  operation  of  the 
refrigerator  is  that  the  wicks  attached  to  the  door  must  be  wrung 
dry  whenever  it  is  opened. 

Put  the  refrigerator  in  a  shady  place  where  the  air  circulates 
freely.  On  dry  hot  days  a  temperature  as  low  as  50°  F.  may  be  ob- 
tained in  one  of  these  coolers.  When  the  air  is  full  of  moisture, 
the  refrigerator  will  not  work  so  well.  Explain  this.  On  such  days 
more  water  will  drip  into  the  lower  pan. 

PROJECT  XXIII.  —  How  to  Make  a  Substitute  for  a  Vacuum  Bottle, 
page  92 

A  very  serviceable  substitute  for  a  vacuum  bottle  may  be  in»d<> 
of  a  three-pound  coffee-tin,  a  small  amount  of  asbestos  insulating 
cement  (such  as  is  used  to  cover  steam  boilers  and  steam  pir*-^, 
a  yard  of  cheesecloth,  and  a  bit  of  flour  or  library  paste,  two  or 
three  old  newspapers,  and  a  Ball-Mason  quart  jar  (Finun  i:>  . 

A  Ball-Mason  quart  jar  measures  7  inches  in  height  and  3  inches 
in  diameter  at  the  base.  An  ordinary  3-pound  «-«.ff.-i-tin  is  about 


594 


EVERYDAY   SCIENCE 


-C 


2  inches  greater  in  diameter  and  a  little  over  2  inches  greater  in 
height.  This  tin  serves  as  the  outside  container.  If  such  a  tin  can- 
not be  had,  procure  a  covered  tin  bucket  of  as  great,  or  greater, 
dimensions. 

Mix  enough  water  with  the  asbestos  insulating  cement  to  make 
a  plastic  paste.     Cover  the  bottom  of  the  tin  with  an  inch  of  this 

f v         paste  (A).    Now  mold  up  a  wall  of 

asbestos  (WW)  of  even  thickness, 
so  as  to  form  a  well  or  nest  7  inches 
deep  and  scant  4  inches  in  diam- 
eter. 

When  the  asbestos  cement  is  dry, 
line  the  well  and  cover  the  top  of 
the  asbestos  wall  with  cheesecloth. 
This  may  be  pasted  on  with  flour 
paste,  rice  paste,  library  paste,  or 
paper-hanger's  paste.  The  latter 
may  be  bought  in  small  cartons  at 
any  paint  store. 

When  the  jar  (B)  is  placed  in  the 
well,  the  top  of  the  jar  should  be 


B 


FIGURE  15.— CROSS  SECTION  OF  even  with  the  top  of  the  asbestos 
INSULATED  BOTTLE.  ^  &nd  there  gh()uld   be  &n  Qpen 


ing    pad;     B,   Ball-Mason 
C,  cover  for  tin- 


WW,  asbestos  wall ;  P,  insulat-  below  the  cover  of  the  can.  To  fill 
this  space,  make  a  newspaper  pad. 
Cut  circular  pieces  of  newspaper  to 
fit  the  space,  until  you  have  enough  to  make  a  pad  of  sufficient 
thickness  to  fill  the  space  (P).  Quilt  them  together  and  cover  the 
pad  with  denim. 

An  insulated  jar  made  in  this  way  will  keep  liquids  hot  or  cold 
for  10  or  12  hours.  A  pint  jar  may  be  insulated  in  a  smaller  con- 
tainer, if  preferred. 

There  are  several  reasons  why  a  Ball-Mason  jar  is  superior  to 
an  ordinary  bottle  in  the  device  described :  it  may  be  tightly 
sealed ;  it  is  less  likely  to  break  when  filled  with  hot  liquids ;  it 


PROJECTS  595 

has  a  large  mouth  and  may  be  easily  washed  and  sterilized ;   if  it 
breaks,  a  duplicate  may  easily  be  had. 

An  insulated  bottle  may  be  made  by  using  a  round  cardboard 
cereal  carton  for  an  outside  container,  newspaper  for  nest  and  pad, 
and  an  ordinary  wide-mouthed  bottle  with  a  tight  cork  for  a  liquid 
container.  Before  pouring  hot  liquid  into  such  a  bottle,  be  sure 
to  heat  the  bottle  by  submerging  it  in  cold  water  and  bringing  the 
water  to  a  boil  (pp.  65  and  66). 

PROJECT  XXIV.  —  Haw  to  Humidify  Indoor  Air  in  Winter, 
page  107 

The  air  in  kitchens  and  bathrooms  is  generally  plentifully  supplied 
with  moisture.  Other  heated  rooms  ordinarily  require  the  addition 
of  considerable  moisture  to  the  air. 

In  case  a  room  is  heated  by  stove,  keep  a  pan  of  water  continuously 
on  the  stove. 

Modern  hot-air  furnaces  are  furnished  with  water  pans  to  supply 
moisture  to  the  air.  If  your  furnace  has  no  such  moisture  supply, 
you  will  have  to  contrive  a  humidifier  best  suited  to  your  needs. 
Where  floor  registers  are  used,  it  is  sometimes  possible  to  set  a  pan 
just  under  the  grating  and,keep  it  filled  with  water.  If  this  cannot 
be  done,  it  may  be  necessary  to  adapt  the  principle  illustrated  in 
Figure  53  of  the  body  of  the  book  to  a  humidifier,  which  may 
be  put  in  some  inconspicuous  place  in  the  room.  Of  course,  the 
nearer  it  can  stand  to  the  warm  air  draft,  the  more  rapidly  the  water 
will  evaporate. 

For  rooms  heated  by  steam  or  hot  water,  have  a  tinsmith  make  a 
galvanized  iron  water  can  of  the  general  shape  indicated  in  Figure 
16.  The  length,  breadth,  and  thickness  of  the  can  will  depend  on 
the  amount  of  space  available  between  the  wall  and  the  radiator. 
At  most  it  need  not  have  a  capacity  of  more  than  2  gallons. 

On  one  of  the  broad  faces  of  the  can  solder  two  No.  10  galvanized 
iron  wires,  as  shown  in  Figure  16,  A  A.  Curve  the  ends  of  these 
wires  so  as  to  hang  them  over  the  connecting  rod  of  the  radiator 
as  means  of  support.  The  distance  between  the  wires  must  be  such 


596 


EVERYDAY   SCIENCE 


that  the  weight  of  the  can  will  be  well  balanced  and  each  wire  will 
fall  between  two  coils  of  the  radiator. 

Bend  two  No.  15  galvanized  iron  wires,  or  a  strip  of  galvanized 
iron  1^  inches  wide,  as  indicated  in  Figure  16,  BB.    These  should 

be  long  enough  to 


B 

B 

f  ~" 

j~V;.v 

f^.  ., 

HI 

have  the   ends    se- 
curely  soldered    to 
the  narrow  sides  of 

^ 

^ 

=•»-£-* 

'•^Bab-2P? 

rUi 

the  can  and  to  ex- 

• 

tend     at     least     6 

» 

L 

inches    above     the 

- 

mouth  of  the  can. 

Fill  the  can  with 

* 

water.       Over    the 

rack    (BB)    hang  a 

double        thickness 

of    canton    flannel, 

A 

A 

rough  side  out,  with 

the  ends  of  the  cloth 

extending  down  into 

the    water    to    the 

* 

>                     < 

•> 

bottom  of  the  can. 

Suspend  the  can  by 

the  curved  wires  to 

the  rear  of  the  radi- 

ator.     The   canton 

v 

flannel  will   absorb 

^ 

s 

the  water  from  the 

can    (see    in    this 

FiGtniE   16.  —  HUMIDIFIER    FOR    STEAM    OR    HOT  connection    Project 
WATER  RADIATOR. 

XXII  and  look  up 

Experiment  97,  p.  325),  and  the  heat  from  the  radiator  will  cause 
rapid  evaporation  from  the  cloth  wicking  as  well  as  from  the 
surface  of  the  water  in  the  can.  Be  sure  to  keep  the  can  sup- 
plied constantly  with  water.  It  will  probably  need  attention  at 
least  once  a  day. 


PROJECTS  597 

PROJECT  XXV.  —  How  to  Operate  a  Refrigerator,  page  1 1 1 

In  operating  a  refrigerator,  there  are  four  things  to  be  kept 
constantly  m  mind :  it  should  have  a  steady  temperature  of  50°  F., 
or  less ;  it  must  have  a  steady  circulation  of  air,  as  shown  in  Figure 
58  of  the  body  of  the  book ;  it  must  remain  dry ;  it  must  be  kept 
spotlessly  clean. 

Low  Temperature.  —  The  low  temperature  of  a  refrigerator  does 
not  necessarily  destroy  germs;  it  prevents  their  multiplying.  If 
food  is  in  good  condition  when  it  is  put  in  an  efficient  refrigerator, 
it  will  remain  in  good  condition.  Before  you  buy  a  refrigerator,  be 
sure  that  it  will  maintain  a  sufficiently  low  temperature.  If  the 
walls  are  properly  insulated  in  the  first  place,  the  joints  tight  and 
secure,  and  the  doors  tight-fitting  and  proof  against  warping,  the 
refrigerator  will  remain  efficient  for  years. 

To  maintain  low  temperature :  (1)  Keep  the  ice  compartment 
full  of  ice.  Incidentally  it  is  cheaper  to  do  this  than  to  maintain  a 
low  supply.  (2)  Keep  drinking  water  in  a  covered  jar,  instead 
of  opening  the  ice  compartment  frequently  to  chip  off  ice.  (3)  Do 
not  leave  any  refrigerator  door  open  a  second  longer  than  necessary. 
If  you  are  removing  food  that  is  to  be  replaced  in  a  few  seconds, 
close  the  door  in  the  meantime. 

Test  the  temperature  of  your  refrigerator  occasionally  with  a 
thermometer.  Leave  the  thermometer  on  each  shelf  in  succession 
for  several  hours.  If  the  temperature  is  much  above  50°  F., 
examine  carefully  the  joints,  doors,  and  locks  for  faulty  insulation. 
Also  see  that  the  drain  pipe  is  clean,  and  that  nothing  is  interfering 
with  the  circulation  of  the  refrigerator.  If  nothing  can  be  dour  to 
keep  the  temperature  low  in  your  refrigerator,  the  safest  and  clicajH 
est  plan  is  to  buy  a  new  one.  An  epidemic  of  intestinal  disease  in 
a  well-known  New  York  hospital  a  few  years  ago  was  traced  in  in- 
efficient refrigerators. 

Air  Circulation.  —  The  air  circulation  explained  and  illustrate  I  on 
page  111  of  this  book  is  of  vital  importance.    It  krcj»  tl'«    in 
terior  of  the  refrigerator  at  a  fairly  even  temperature  and  helps 
to  keep  it  dry.     Moreover,  the  circulating  air  collects  the  odors 


598  EVERYDAY  SCIENCE 

and  impurities  and  deposits  them  on  the  ice,  whence  they  are 
carried  out  by  the  melting  ice  through  the  drain  pipe. 

It  follows,  therefore,  that  delicacies,  such  as  milk,  cream,  and 
butter,  should  be  put  where  the  air  fresh  from  the  ice  strikes  them. 
Meats  and  other  such  foods  should  come  next.  Vegetables,  fruit, 
cheese,  fish,  or  any  other  foods  that  emit  strong  odors,  should  be 
last  in  the  circulatory  system,  so  that  the  odors  will  be  deposited  on 
the  ice  without  tainting  the  more  delicate  foods.  Even  with  this 
arrangement,  all  highly  odorous  foods  should  be  kept  covered.  Two 
or  three  pieces  of  charcoal  scattered  through  the  refrigerator  and 
changed  two  or  three  times  a  month  will  help  to  absorb  odors. 
Large  cafes  have  a  separate  refrigerator  for  each  kind  of  food. 

Do  not  stuff  any  shelf  so  full  of  foods  as  to  impair  the  circulation 
of  air.  As  soon  as  the  circulation  of  cold  air  is  cut  off,  the  tem- 
perature of  the  refrigerator  rises  and  moisture  collects  —  two 
conditions  favorable  for  germ  life. 

Do  not  put  any  kind  of  food  on  the  ice.  It  may  impair  the 
circulation  of  air;  but  more  important  than  this,  it  will  gather 
the  odors  and  impurities  that  should  be  deposited  on  the  ice. 

Dryness.  —  Keep  a  little  salt  in  an  open  dish  in  your  refrigerator. 
If  this  becomes  damp  or  sticky,  examine  your  refrigerator,  as  has 
been  suggested  in  the  case  of  too  high  temperature.  High  tem- 
perature and  dampness  generally  go  along  together  in  a  refrigerator. 

Foods  that  you  wish  to  keep  moist  or  liquids  that  you  wish  to 
keep  from  evaporating  should  be  kept  in  tightly  covered  vessels. 

Cleanliness.  —  Keep  your  refrigerator  spotlessly  clean.  A  porce- 
lain enameled  lining  without  joints  or  seams  is  most  satisfactory 
and  safest.  Don't  allow  a  single  drop  of  milk  or  speck  of  food  to 
remain  on  the  shelves  of  your  refrigerator,  as  breeding  places  for 
germs.  Keep  the  interior  wiped  out  with  water  clean  enough  to 
drink  and  a  cloth  or  sponge  clean  enough  to  wash  your  face  with. 
Wipe  all  milk  bottles,  especially  the  caps  and  tops,  with  a  clean 
damp  cloth  before  putting  them  into  the  refrigerator. 

Once  a  week  wash  the  interior  with  soap  and  water,  wipe  it  out 
with  clear  water  afterwards,  and  dry  it  with  a  dish  towel.  Cleanse 
the  ice  compartment  and  flush  the  drain  with  a  strong  solution  of 


PROJECTS 


599 


washing  soda.  After  cleaning  the  refrigerator,  replace  the  ice 
and  close  the  doors  for  a  while  before  replacing  the  food.  An 
iced  refrigerator  dries  much  more  quickly  with  the  doors  shut  than 
an  un-iced  refrigerator  will  dry  with  the  doors  open. 


PROJECT  XXVI.  —  How  to  Install  Devices  for   Ventilating,  pages 
113-114 

Full  instructions  are  given  on  pages  113-114  for  making  ventilat- 
ing boards  and  screens.  Measurements  must  depend  dn  the  size 
of  the  window  to  be  fitted. 

In  the  case  of  cloth  screens,  the  simplest  way  to  get  measure- 
ments is  simply  to  duplicate  the  frame  of  the  summer  screen  and 
then  substitute  muslin  for  wire  screening. 

PROJECT  XXVII.  —  How  to  Siphon  Cream  from  a  Bottle  of  Milk, 
page  119 

To  remove  cream  from  a  bottle  of  milk  with  a  spoon  or  patent 
cream  dipper  is  a  difficult  and  often  a  wasteful  operation.  The 
cream  or  top  milk  may 
be  much  more  easily 
and  effectively  removed 
with  a  glass  siphon. 

Bend  a  piece  of  glass 
tubing  in  the  labora- 
tory into  the  form  of 
a  siphon  (Figure  17). 
Have  the  two  arms  of 
the  siphon  close  enough 
together  so  that  the 
loop  may  be  inserted  in 
a  milk  bottle  as  shown 
in  A,  Figure  17. 


FIOCBE  17. 


si,    m:A£ti&v    AI.  ^ 

To  start  the  action  of  the  siphon,  dip  the  short  arm  of  the  sipno 
into  the  cream,  as  in  A,  Figure  17,  allowing  the  cream  to  run  in  ar 
fill  the  short  arm,  and  the  long  arm  to  the  depth  of  the  short  arm. 


600  EVERYDAY  SCIENCE 

Now  hold  the  thumb  over  the  opening  of  the  long  arm  and  place  the 
siphon  in  position,  as  in  B,  Figure  17. 

Adjust  the  end  of  the  short  arm  to  whatever  depth  you  wish, 
place  a  receiving  vessel  under  the  opening  of  the  long  arm,  and 
remove  your  thumb  from  the  opening  of  the  long  arm  (Figure 
170. 

The  siphon  may  be  cleansed  by  running  warm  (not  hot)  soapy 
water  through  it  and  rinsing  with  clear  warm  water. 

PROJECT  XXVIII.  —  How  to   Use  the  Most  Common  Solvents  to 
Remove  Stains,  page  140 

* 

Gasoline.  —  This  is  the  most  common  solvent  for  sponging  out 
grease  or  oil  stains.  The  most  delicate  fabrics  may  be  soaked  or 
washed  hi  it  without  risk.  It  should  be  used  either  out  of  doors  or 
in  a  well- ventilated  room,  without  flame  or  smoldering  spark  of  fire 
or  even  a  hot  iron  in  the  room.  Never  use  a  hot  iron  on  goods 
cleaned  with  gasoline  until  the  fabric  has  been  hung  out  long 
enough  for  all  the  gasoline  to  evaporate. 

After  using  gasoline,  give  the  fumes  plenty  of  time  to  pass  out 
before  you  light  any  sort  of  fire.  Remember  it  is  the  volatile 
vapor  of  gasoline  that  is  so  dangerously  inflammable. 

To  remove  grease  from  delicately  colored  fabrics,  chloroform, 
ether,  and  benzine  are  superior  to  gasoline  because  they  evaporate 
more  rapidly  and  are  less  likely  to  leave  a  "ring."  Chloroform  and 
ether  are  the  best,  but  also  the  most  expensive. 

Probably  the  best  fabric  for  applying  stain  solvents  is  clean  cheese- 
cloth. 

Gasoline  is  sometimes  mixed  with  carbon  tetrachloride,  another 
effective  solvent  of  grease,  and  sold  under  a  trade  name  such  as 
"Carbona."  The  great  advantage  of  such  a  -mixture  is  that  its 
vapor  is  not  inflammable. 

Turpentine.  —  (1)  Paint  and  Varnish.  —  Turpentine  will  remove 
wet  paint  or  varnish  very  easily  from  any  fabric.  If  used  with  suffi- 
cient patience  and  perseverance,  it  will  also  remove  dry  paint  from 
any  fabric.  After  the  paint  is  removed,  sponge  with  chloroform 


PROJECTS  601 

to  remove  the  turpentine.  Alcohol  followed  by  chloroform,  or 
chloroform  alone,  will  often  remove  paint  or  varnish  from  delicate 
fabrics. 

(2)  Tar  or  Wagon  Grease.  —  Rub  lard  into  the  stain  to  soften  it. 
Wet  with  turpentine.     Gently  scrape  off  all  loose  particles  with  a 
knife.     Wet  again  and  again  with  turpentine  and  continue  to  scrape 
until  all  loose  particles  have  been  removed.     Then  sponge  with 
turpentine  and  rub  gently  with  a  clean  cloth  until  the  fabric  is 
dry.     Sponging  with  chloroform  will  remove  the  turpentine  and 
restore  the  color  if  it  is  affected. 

For  such  stains  on  white  wash  goods,  rub  lard  on  the  stain,  wet 
with  turpentine,  and  after  several  hours  wash  with  soap  and  warm 
water.  On  heavy  goods  use  a  brush. 

(3)  Vaseline.  —  If  sponging  with  turpentine  fails,  try  sponging 
with  ether. 

(4)  Hardened  Paint  Brushes.  —  (a)  Soak  for  24  hours  hi  raw 
linseed  oil.     Rinse  in  hot  turpentine.     Repeat,  if  necessary. 

(6)  Heat  vinegar  to  the  boiling  point  and  allow  the  brushes  to 
stand  hi  it. 

(c)  Soak  the  brushes  in  paint  and  varnish  remover,  which  may 
be  bought  at  any  paint  store. 

N.  B.  —  Brushes  should  never  be  allowed  to  dry  hard.  They 
should  be  kept  suspended  —  never  resting  on  the  bristles  —  in  raw 
linseed  oil.  A  good  way  to  suspend  brushes  is  to  bore  small  holes 
through  the  tips  of  the  handles,  thread  them  on  a  wire  stretched  be- 
tween two  nails  and  allow  the  brushes  to  be  submerged  in  the  oil  to  a 
depth  of  at  least  5  inch  above  the  ferrule  or  binding  strap. 

PROJECT  XXIX.  —  How  to  Prevent  Tea-kettle  Scale,  page  144 

If  a  tea-kettle  is  given  the  daily  attention  that  any  other  kitchen 
utensil  or  cooking  vessel  receives,  there  will  be  no  accumulation  of 
scale.  Tea-kettle  scale  is  unsightly  but  in  no  wise  harmful.  The 
principal  reason  why  it  should  not  be  allowed  to  accumulate,  or 
should  be  removed  if  it  is  allowed  to  accumulate,  is  that  it  CHUM  s 
such  a  waste  of  fuel.  This  is  not  noticeable  if  the  kettle  is  set  all  day 


602  EVERYDAY   SCIENCE 

over  a  coal  fire,  but  the  waste  is  considerable  if  measured  gas  is 
the  fuel  used.  It  has  been  estimated  that  certain  kinds  of  scale 
offer  from  twenty  to  fifty  times  the  resistance  to  heat  that  is  offered 
by  an  equal  thickness  of  wrought  iron. 

If  the  tea-kettle  is  washed  daily,  or  even  three  times  a  week, 
and  scoured  if  necessary  with  Bon  Ami  or  Old  Dutch  Cleanser, 
scale  will  not  accumulate. 

Housekeepers  who  will  not  exercise  this  care,  may  put  a  piece  of 
limestone,  rough  marble,  or  oyster  shell  in  the  tea-kettle.  Change 
it  for  a  fresh  piece  two  or  three  times  a  month. 

PROJECT  XXX.  —  How  to  Remove  Tea-kettle  Scale,  page  144 

Heavy  Iron  Kettles.  —  To  remove  accumulated  scale  from  a 
heavy  iron  kettle,  fill  the  kettle  with  cold  water  and  add  a  heaping 
tablespoonful  of  sal  ammoniac.  Bring  this  to  a  boil  and  then 
empty  the  kettle.  Place  the  empty  kettle  over  a  flame  until  it  is 
very  hot  and  the  scale  will  peel  off.  Set  the  kettle  aside  and  allow 
it  to  cool  slowly.  Repeat  if  necessary.  After  the  scale  has  been 
removed  and  the  kettle  is  cool,  fill  it  with  a  strong  solution  of  wash- 
ing soda,  boil,  and  rinse  with  clear  hot  water. 

Aluminum  Kettles.  —  In  the  case  of  an  aluminum  kettle,  fill 
with  cold  water,  and  add  a  heaping  tablespoonful  of  oxalic  acid 
crystals.  Boil  the  solution,  let  it  stand  all  night,  and  boil  again  in 
the  morning.  This  will  remove  a  thin  scale,  but  the  operation  will 
have  to  be  repeated  several  times  for  a  heavy  scale.  Afterwards 
wash  the  kettle  thoroughly  with  ordinary  soap  and  warm  water 
and  rinse  with  clear  hot  water  to  remove  all  trace  of  the  poisonous 
acid. 

Concentrated  nitric  acid  will  remove  the  scale  from  aluminum 
much  more  quickly  than  oxalic  acid,  without  injuring  the  aluminum. 
But  it  has  to  be  handled  so  carefully  that  it  is  not  recommended 
for  ordinary  household  use. 

Strong  alkalies  dissolve  aluminum.  Never  use  them  on  that 
metal  for  any  purpose. 

Enamel  Kettles.  —  Scale  does  not  tend  to  accumulate  so  rapidly 


PROJECTS  603 

on  good  enamel  ware.  Keep  an  enamel  kettle  clean  by  washing 
it,  or  boiling  it  if  necessary,  frequently  with  a  strong  solution  of 
washing  soda.  Either  oxalic  acid  or  nitric  acid  will  remove  scale 
from  enamel  ware  without  "eating"  through  the  enamel,  but  any 
strong  acid  will  remove  the  high  polish  from  the  surface  of  enamel. 

PROJECT  XXXI.  —  How  to  Soften  Hard  Water  for  Domestic  Use, 
page  146 

Water  of  temporary  hardness  does  not  offer  a  serious  problem 
because  it  can  be  softened  by  boiling.  Permanently  hard  water 
requires  something  more  to  soften  it. 

For  Laundry  Use.  —  Washing  soda  is  the  most  common  softener 
for  laundry  purposes.  The  two  mistakes  commonly  made  in  its  use 
must  be  guarded  against :  do  not  make  too  strong  a  solution ;  and 
be  sure  that  the  soda  is  thoroughly  dissolved.  A  failure  to  observe 
these  cautions  may  result  in  injury  to  the  clothes. 

Dissolve  1  pound  of  washing  soda  in  a  quart  of  hot  water.  For 
most  hard  waters,  2  tablespoonfuls  of  this  solution  will  soften  a 
gallon  of  water.  If  the  water  is  unusually  hard,  more  of  the  solution 
will  be  required. 

For  Delicate  Fabrics.  —  Borax  is  much  to  be  preferred  to  washing 
soda  as  a  water  softener  because  it  will  do  no  injury  either  to  the 
hands  or  to  delicate  fabrics.  It  is  so  expensive,  however,  that  it 
cannot  be  used  in  great  abundance.  To  soften  water  for  washing 
delicate  fabrics,  dissolve  1  tablespoonful  of  borax  in  a  cup  of  hot 
water.  This  will  soften  a  gallon  of  water. 

For  Toilet  Purposes.  —  (a)  Borax  used  as  suggested  in  the  preced- 
ing paragraph  will  soften  water  satisfactorily  for  toilet  uses. 

(6)  The  addition  of  the  juice  of  one  or  two  lemons  to  a  bowl  of 
hard  water  softens  it  agreeably  for  washing  or  rinsing  the  hair. 

PROJECT  XXXII.  —  How  to  Read  a  Water-meter  or  Gas-meter  Dial, 

pages  200-206 

Water  is  sometimes  sold  to  the  consumer  at  a  flat  rate  by  the 
month  or  year.  In  such  cities  there  is  no  direct  measurement  of 


604 


EVERYDAY   SCIENCE 


the  amount  of  water  a  consumer  uses.  In  other  cities  water  is 
sold  at  so  much  per  1000  gallons,  and  the  quantity  used  by 
each  consumer  is  measured  by  a  meter  on  the  consumer's  premises. 
Water-meters  are  pretty  accurate  instruments.  If  they  are  out  of 
order,  they  are  most  likely  to  record  less  water  than  is  actually  used. 
It  is  convenient  to  know  how  to  read  the  dial  of  your  water- 
meter.  If  it  is  a  direct-reading  dial,  no  instruction  is  needed.  Most 
.water-dials,  however,  are  like  the 
dial  shown  in  Figure  18,  and  re- 
quire some  explanation. 

On  this  dial  the  unit  of  meas- 
urement is  the  cubic  foot.  The 
hands  revolve  about  circles.  The 
numbering  on  each  circle  indicates 
the  direction  the  hand  of  that 
circle  travels.  On  the  dial  shown 
in  Figure  18,  the  hands  in  the 
100,000,  1000,  and  10  circles 
travel  contrary  to  the  hands  of  a 
clock.  The  alternate  hands  travel 
in  the  direction  of  clock-hands. 
The  number  on  the  outside  of 


FIGURE  18.  —  -  ,  .       . 

METER.  of  cubic   feet  recorded    for    one 

complete  revolution  of   the  hand. 

Each  circle  has  10  divisions  ;  each  division  thus  indicates  -fa  of  the 
total  for  the  circle.  (In  reading  the  dial,  pay  no  attention  to  the 
circle  measuring  1  foot.  It  is  used  for  test  purposes,  as  will  be 
explained  later.) 

The  reading  of  the  dial  in  Figure  18  is  as  follows  : 

1st  hand  shows  ^  of  100,000,  or  10,000  cu.  ft. 
2d  hand  shows  TV  of  10,000,  or  1,000  cu.  ft. 
3d  hand  shows  &  of  1,000,  or  800  cu.  ft. 
4th  hand  shows  A  of  100,  or  60  cu.  ft. 
5th  hand  shows  T75  of  10,  or  7  cu.  ft. 


PROJECTS  605 

Caution.  —  Notice  that  when  a  hand  is  between  two  figures,  the 
lesser  is  read,  just  as  in  the  case  of  the  hour-hand  of  a  clock.  If  the 
hand  is  very  near  a  figure,  and  you  do  not  know  whether  it  is  just 
short  of  the  figure  or  just  past  the  figure,  the  following  circle  will 
guide  you.  For  example  a  careless  observer  might  read  the  2d 
circle  2000.  If  it  were  2000,  then  the  hand  in  the  3d  circle  would 
have  reached  0  or  passed  it.  Since  the  hand  in  the  3d  circle  has  not 
quite  reached  0,  the  2d  dial-hand  is  to  be  read  1000  instead  of 
2000.  In  other  words,  think  of  the  dial  hand  which  shows  a  doubt- 
ful reading  as  the  hour-hand  of  a  clock,  and  the  dial-hand  of  the 
following  circle  as  the  minute-hand.  If  the  "minute-hand"  has 
completed  a  revolution  and  points  to  0  or  beyond,  read  the  figure 
toward  which  the  "hour-hand"  is  pointing.  If  the  "minute-hand" 
has  not  quite  reached  0,  read  the  lesser  figure  preceding  the  "hour- 
hand." 

It  can  be  seen  that  a  quick  way  to  read  the  dial  is  to  begin  with 
the  10  circle  and  put  the  figures  down  in  reverse  order.  Thus,  the 
10  circle  records  units,  the  100  circle  tens,  the  1000  circle  hundreds, 
etc. 

Commercially,  one  cubic  foot  is  equal  to  7  gallons,  and  so  if  you 
wish  to  reduce  cubic  feet  to  gallons,  multiply  by  7. 

The  dial  cannot  be  set  back  to  0  after  reading.  The  record 
is  continuous.  To  ascertain  the  amount  of  water  used  in  June, 
for  example,  you  would  have  to  subtract  the  reading  taken  on  the 
31st  of  May  from  the  reading  taken  on  the  30th  of  June.  You  can 
also  ascertain  the  amount  of  water,  used  for  any  single  purpose, 
such  as  sprinkling  the  lawn,  by  taking  the  readings  before  and  after 
using  the  water. 

If  you  suspect  that  water  is  being  wasted  through  some  Irak, 
close  all  outlets  tight,  and  observe  the  circle  on  the  dial  marked 
"one  foot."  If  it  continues  to  move,  there  is  a  leak  somewhere 
on  your  premises,  since  the  meter  can  register  only  when  water  is 
passing  through  it. 

A  gas-meter  does  not  record  any  number  of  cubic  feet  smaller  than 
hundreds.  Consequently,  the  last  two  circles  on  a  water-meter, 
recording  tens  and  units,  are  missing  on  a  gas-meter. 


606  EVERYDAY  SCIENCE 

The  reading  on  the  gas-meter  shown  in  Figure  19  is  79,500  cubic 
feet.  The  hand  in  the  first  circle  presents  a  fine  example  of  a 
doubtful  reading.  It  looks  as  if  it  might  be  exactly  80,000  cubic 
feet.  But  since  the  hand  in  the  2d  circle  has  not  quite  reached 


FIGURE  19.  —  DIAL  OF  GAS-METER. 

zero,  the  first  hand  must  be  read  7  and  the  second  hand  9  —  giving 
79  instead  of  80  thousand. 

The  circle  marked  "two  feet"  is  for  test  purposes,  as  was  ex- 
plained in  the  case  of  the  water-meter. 

PROJECT  XXXIII.  —  Learning  Weather  Lore  That  a  Boy  Scout  or 
Camp  Fire  Girl  Ought  to  Know,  Chdpter  VIII. 

Careful  observation  of  sky  and  clouds  for  centuries,  of  air  condi- 
tions, and  of  the  behavior  of  birds,  barnyard  fowls,  and  insects, 
has  resulted  in  a  wealth  of  weather  maxims  that  are  pretty  reliable. 
Of  course  there  are  many  bits  of  superstition  that  pass  as  weather 
lore  that  are  utterly  unreliable.  The  task  for  an  observer  is  to 
sort  out  weather  wisdom  from  silly  superstitions.  The  most  useful 
and  interesting  books  for  the  amateur  weather  forecaster  are : 

"Official  Handbook,  Boy  Scouts  of  America." 

"Reading  the  Weather,"  T.  M.  Longstreth.  Outing  Publishing 
Co. 


PROJECTS  607 

"American  Boys'  Book  of  Signs,  Signals,  and  Symbols,"  Dan 
Beard.  J.  B.  Lippincott  Co. 

"The  Wonder  Book  of  the  Atmosphere,"  E.  J.  Houston. 
Frederick  A.  Stokes  Co. 

"  Practical  Hints  for  Amateur  Forecasters,"  P.  R.  Jameson. 
Taylor  Instrument  Companies,  Rochester. 

"Weather  Lore,"  Richard  Inwards. 

Study  the  folk-signs  as  well  as  the  scientific  signs  of  weather, 
and  report  from  time  to  time  on  the  reliability  of  these  signs. 
Some  of  the  most  interesting  and  trustworthy  signs  are  here 
given : 

Clouds  and  Sky.  —  White  feathery  wisps  of  clouds,  like  spreading 
locks  of  hair,  five  or  six  miles  above  the  earth  are  cirrus  clouds. 
When  these  appear  suddenly,  especially  with  the  ends  of  the  feathers 
turned  upwards,  showing  that  they  are  falling,  they  indicate  rain 
to  come  within  two  or  three  days. 

Very  large  low-hanging  cumulus  clouds  (p.  103)  indicate  violent 
storms  in  the  immediate  future.  Such  clouds  seldom,  if  ever, 
appear  without  an  electric  display. 

When  the  blue  sky  is  obscured  by  a  delicate  veil  of  white,  indi- 
cating a  thin  mist  high  overhead,  rain  is  indicated.  This  veil  is 
known  as  a  cirropallium. 

Small,  dark  clouds  scurrying  along  below  the  big  clouds  mean 
rain. 

When  the  sky  is  overcast  with  thick,  gray  clouds  with  lumpy 
lower  surfaces  "like  the  inverted  tops  of  a  pan  of  buns,"  a  steady 
rain  is  indicated. 

A  pink  sunrise  indicates  fair  weather,  as  does  a  ruddy  sunset. 
But  a  ruddy  sunrise  or  a  pale  yellow  morning  sky  indicates  rain. 
A  bright  yellow  morning  sky  indicates  wind.  A  great  deal  of 
weather  wisdom  is  wrapped  up  in  the  old  maxim : 

"Evening  red  and  morning  gray 
Will  set  the  traveler  on  his  way ; 
But  evening  gray  and  morning  red 
Will  bring  down  showers  on  his  head." 


608  EVERYDAY  SCIENCE 

Air  Conditions. —  When  all  kinds  of  odors  are  more  noticeable,  and 
smoke  descends  instead  of  rising,  there  are  good  prospects  of  rain. 

When  no  dew  appears  on  the  grass  in  the  morning,  rain  is  prob- 
ably indicated. 

If  raindrops  cling  to  leaves  and  twigs  instead  of  drying  quickly, 
there  will  probably  be  more  rain. 

Birds  and  Fowls.  —  When  migratory  birds  fly  south  earlier 
than  usual,  an  early  cold  winter  is  indicated. 

When  birds  capable  of  long  flights  remain  close  to  their  nests, 
wind  and  rain  may  be  looked  for. 

Guinea  fowls  raise  a  great  clamor  before  a  rain. 

Chickens  roll  and  flutter  in  the  dust  before  a  rain. 

Crows  fly  low  and  wheel  in  great  circles,  cawing  raucously,  be- 
fore a  rain.  But  if  they  fly  high  in  pairs,  continued  fair  weather 
may  be  expected. 

Gulls  circle  around  at  great  heights,  emitting  sharp  cries  as  of 
distress,  before  a  rain. 

Insects.  —  When  spiders  are  seen  crawling  about  more  than 
usual  on  walls,  rain  will  soon  come.  This  is  a  reliable  sign,  especially 
in  the  months  of  winter  rains. 

When  spiders  spin  new  webs  or  cleanse  their  old  ones,  expect  fair 
weather.  If  they  continue  spinning  during  a  rain,  the  rain  will  soon 
be  over. 

When  flies  or  gnats  are  more  than  ordinarily  troublesome,  ex- 
pect rain  or  a  drop  of  temperature. 

When  flies  cling  to  the  ceiling  or  disappear,  rain  is  to  be  expected. 

PROJECT  XXXIV.  —  How  to  Remove  Stains  with  Absorbents, 
page  325 

The  principle  of  capillarity  illustrated  in  Experiment  97  is  applied 
in  the  removal  of  stains  from  the.  most  delicate  garments.  The 
use  of  absorbents,  such  as  blotting  paper,  French  chalk  (which  is 
ground  soapstone),  pipe  clay,  fuller's  earth,  common  starch,  and 
melted  tallow,  is  the  simplest  and  least  risky  method  of  removing 
grease,  wax,  blood,  and  scorch  stains. 


PROJECTS  609 

Mention  has  been  made  in  Projects  IX  and  XXVIII  of  the  use 
of  absorbents  for  the  removal  of  ink  and  tar. 

Grease.  —  (a)  Cover  the  spot  with  fuller's  earth,  pipe  clay,  or 
French  chalk.  Put  a  sheet  of  brown  paper  over  this  and  press 
with  an  iron  that  is  warm  but  not  hot  enough  to  scorch  or  change 
the  color  of  goods. 

(6)  Mix  a  paste  of  French  chalk  or  fuller's  earth  with  water  and 
place  it  over  the  spot.  Allow  this  to  stand  for  several  days  and  then 
brush  it  off.  Repeat  if  necessary. 

(c)  Put  a  piece  of  blotting  paper  under  the  spot  and  another 
over  it.  Put  a  warm  iron  on  the  top  blotter.  Keep  changing  the 
blotters  until  all  the  grease  has  been  absorbed.  Sponge  the  spot 
lightly  with  chloroform  or  ether  if  necessary.  • 

Mud  on  Delicate  Fabrics.  —  Wait  until  the  mud  dries.  Gently 
remove  the  loose  particles.  Make  a  paste  of  boiled  starch.  Lay 
this  over  the  stain  and  let  it  dry  thoroughly.  Brush  it  cfff  carefully. 
Repeat  if  necessary. 

Scorch.  —  Make  a  paste  of  boiled  starch  and  use  as  in  case  of 
mud  stain. 

Blood.  —  Make  a  paste  of  common  starch  and  warm  water. 
Apply  it  to  the  stain,  allow  it  to  dry  thoroughly,  and  remove  by 
brushing  gently. 

Wax.  —  Gently  remove  all  the  wax  possible  from  the  surface 
of  the  fabric  with  a  penknife.  Put  a  piece  of  brown  paper  under 
the  fabric.  Cover  the  spot  with  a  paste  of  starch  or  French  chalk 
and  water.  Lay  another  piece  of  brown  paper  over  this  and  press 
with  a  warm  iron. 

Machine  Oil  on  Wash  Goods.  —  Cover  the  spot  with  lard  and 
allow  it  to  stand  several  hours.  Wash  in  cold  water  with  soap. 

PROJECT  XXXV.  —  How  to  Prepare  Soil  for  Planting  a  Liwu. 
pages  307-339 

"The  ideal  soil  for  grasses  best  suited  for  lawn  making  is  «>nf 
which  is  moderately  moist  and  contains  a  considerable  percentage 
of  clay —  a  soil  which  is  somewhat  retentive  of  moisture,  but  never 


610  EVERYDAY   SCIENCE 

becomes  excessively  wet,  and  is  inclined  to  be  heavy  and  compact 
rather  than  light,  loose,  and  sandy.  A  strong  clay  loam  or  a  sandy 
loam  underlaid  by  a  clay  subsoil  is  undoubtedly  the  nearest  approach 
to  an  ideal  soil  for  a  lawn ;  it  should,  therefore,  be  the  aim  in  es- 
tablishing a  lawn  to  approach  as  near  as  possible  to  one  or  the  other 
of  these  types  of  soil."  Farmers'  Bulletin  No.  494,  United  States 
Department  of  Agriculture. 

Since  one  does  not  choose  his  home  site  for  the  quality  of  the 
soil,  it  is  clear  that  the  soil  in  his  yard  may  not  be  particularly 
adapted  to  the  raising  of  a  good  lawn.  Since  the  lawn  is  intended 
to  be  a  permanent  feature  of  the  decoration  of  the  place,  it  is 
worth  while  to  do  all  in  one's  power  to  improve  the  condition  of 
the  soil. 

If  one  builds  a  house  and  is  compelled  to  haul  in  soil  to  fill  and 
grade  his  premises,  he  can  at  least  exercise  care  not  to  have  the 
wrong  kind  of  filling.  If  the  soil  is  of  excellent  quality  for  lawn 
purposes,  it  may  be  necessary  for  the  owner  to  guard  against  having 
the  surface  soil  covered  with  subsoil  taken  from  the  excavation 
for  the  foundation.  Never  allow  soil  that  is  full  of  bricks,  this, 
boards,  and  other  building  debris  to  be  dumped  into  your  yard  even 
for  subsoil.  Such  debris  interferes  both  with  drainage  and  with 
upward  capillary  movement  of  water  in  dry  weather. 

It  is  almost  impossible  to  grow  a  lawn  of  any  sort  in  coarse,  sandy 
soil  and  it  is  very  difficult  to  keep  a  lawn  in  good  condition  which 
has  a  sandy  subsoil.  To  make  a  satisfactory  lawn  where  the  soil 
is  sandy,  add  a  top  dressing  of  two  or  three  inches  of  clay  and  work 
it  into  the  top  four  to  six  inches  of  sand.  If  a  mixture  of  loam  and 
well-rotted  manure  can  be  laid  over  this  to  the  depth  of  two  or  three 
inches,  a  very  satisfactory  lawn  soil  will  be  obtained. 

If  the  soil  is  too  heavy  or  sour  for  lack  of  drainage,  mix  a  layer  of 
sand  or  finely  sifted  ashes  with  the  heavy  soil,  at  the  same  time 
adding  humus  to  help  fertilize  as  well  as  coarsen  the  soil. 

Soil  should  be  prepared  for  a  lawn  to  the  depth  of  8  or  10  inches, 
even  though  the  surface  seed  bed  need  not  be  more  than  1  inch  in 
depth.  In  spading  a  soil  that  is  not  deep,  be  careful  not  to  turn 
the  subsoil  over  the  surface  soil.  After  the  soil  has  been  spaded, 


PROJECTS  611 

rake  it  fine,  then  compact  it  with  a  lawn  roller,  and  finally  loosen  a 
shallow  surface  bed  for  the  reception  of  the  seed. 

Grass  should  be  sowed  in  the  late  fall  or  the  early  spring.  If 
in  the  fall,  September  and  October  are  the  favorable  months,  de- 
pending on  the  time  when  the  fall  rains  set  in.  It  is  not  well  to  do 
the  seeding  during  a  dry  period,  unless  one  has  at  his  disposal  arti- 
ficial means  for  watering.  Fall  planting  has  the  advantage  of  allow- 
ing a  number  of  weeds  to  germinate  and  be  killed  by  the  frosts. 

In  localities  where  there  is  low  winter  temperature  and  little 
snow,  fall  planting  is  not  so  successful.  In  such  cases,  the  soil 
should  be  prepared  in  the  fall  so  as  to  allow  the  weed  seed  to  ger- 
minate and  the  young  weeds  to  be  killed.  Then  sow  to  grass  seed 
as  soon  as  the  soil  can  be  broken  up  in  the  spring  and  in  time  to 
get  the  benefit  of  the  warm  rains  of  early  spring. 

PROJECT  XXXVI.  —  How  to  Prepare  Soil  for  the  Home  Vegetable 
or  Flower  Garden,  pages  307-339 

Loam  is  the  best  garden  soil.  It  needs  practically  no  modification 
except  the  liberal  addition  of  manure  or  artificial  fertilizer.  As 
much  as  600  pounds  of  manure  a  year  may  be  applied  with  advan- 
tage to  a  garden  plot  20  feet  square.  Coarse  manure  should  be 
applied  in  the  fall  and  thoroughly  spaded  under.  In  the  spring, 
fine,  well-rotted  manure  should  be  applied  just  before  spading. 
This  spring  spading  should  work  the  soil  to  a  depth  of  10  or  12 
inches.  Carefully  fine  the  soil  as  deep  as  possible  with  a  rake  and 
smooth  the  surface  for  laying  off  into  rows.  Tomatoes,  eggplants, 
and  other  plants  that  require  long  growing  seasons  are  materially 
benefited  by  an  application  of  well-rotted  manure  between  rows 
when  the  plants  are  about  half-grown. 

But  the  back-yard  gardener  cannot  choose  his  soil.  He  may  have 
light,  sandy  soil  or  heavy  compact  clay  instead  of  the  desirable 
loam.  Much  can  be  done  in  either  case  to  improve  the  garden 
plot.  The  sandy  soil  needs  the  addition  of  abundant  manure  to  en- 
rich it  and  to  make  it  more  retentive  of  moisture.  If  a  supply  of 
moisture  is  lacking,  the  best  substitute  is  compost.  Every  gardener 


612  EVERYDAY   SCIENCE 

should  have  a  compost  heap.  .  This  is  a  pile  of  waste  organic  mate- 
rial prepared  from  six  to  twelve  months  before  using  on  the  garden. 

In  every  household  there  is  a  waste  of  garden  rubbish,  leaves, 
grass  mowed  from  the  lawn,  parings  and  other  unused  portions  of 
fruits  and  vegetables.  These  should  all  be  thrown  on  the  compost 
heap  to  decay.  Be  sure  to  avoid  throwing  diseased  plants  and 
weeds  bearing  ripe  seeds  on  the  pile.  But  do  not  burn  your  leaves 
in  the  fall.  Bury  them  on  the  compost  heap  and  let  them  rot  for 
fertilizer.  The  compost  heap  should  be  built  in  alternate  layers 
of  vegetable  refuse  and  earth.  Every  six  or  eight  inches  of  organic 
matter  should  be  covered  with  an  inch  or  so  of  soil.  The  burying 
helps  to  rot  the  vegetable  matter.  You  will  find  it  convenient  to 
make  the  heap  not  more  than  six  feet  square  and  about  four  feet 
high.  It  is  easier  to  make  the  sides  of  a  small  pile,  such  as  this, 
perpendicular  and  to  keep  the  top  flat  for  the  reception  and  reten- 
tion of  moisture  to  aid  in  rotting.  If  this  is  forked  over  once  or 
twice  in  the  late  fall  and  again  in  the  early  spring,  decay  will  be 
hastened.  In  the  spring,  spread  it  on  the  garden  plot  like  manure 
and  spade  it  under. 

Heavy  clay  soil  may  need  the  addition  of  sifted  ashes  from  which 
all  clinkers  have  been  removed  in  order  to  loosen  its  texture.  Soil 
that  has  long  been  uncultivated  or  that  has  been  devoted  to  lawn 
is  likely  to  be  sour.  The  presence  of  plantain  or  sorrel  generally 
indicates  sourness.  Clay  soil  because  of  its  compactness  and  poor 
drainage  is  apt  to  be  in  this  condition.  To  remedy  this,  a  small 
amount  of  some  base  to  neutralize  the  acid  is  needed.  Apply  evenly 
over  the  garden  plot,  when  you  are  preparing  the  seed  bed  in  the 
spring,  1  pound  of  air-slaked  lime,  2  pounds  of  ground  limestone,  or 
2  pounds  of  unleached  wood  ashes 1  to  every  30  square  feet.  Rake 
this  into  the  soil  to  the  depth  of  2  inches.  Be  sure  to  do  this  after 
the  spring  fertilizer  has  been  worked  into  the  soil,  not  at  the  same 
time.  Liberal  use  of  manure  and  compost  helps  to  loosen  clay  soil 
and  to  make  it  more  workable. 

!Wood  ashes  have  notable  manurial  value  because  of  potash  salts 
contained ;  but  lose  most  of  this  value  if  subjected  to  the  action  of  water 
(leached). 


PROJECTS  613 

PROJECT  XXXVII.  —  How  Boy  Scouts  and  Other  Campers  May 
Prevent  Forest  Fires,  Forestry  Rules,  pages  339-346 

Every  camper  should  obtain  a  copy  of  the  laws  of  his  state  re- 
garding the  conservation  of  forests.  If  a  legal  permit  to  build 
a  fire  in  forests  is  required  of  all  campers,  such  a  permit  should  be 
secured  by  all  means.  The  following  is  a  copy  of  the  notice  posted 
in  forests  by  the  United  States  Department  of  Agriculture.  It 
directs  attention  to  United  States  laws  on  this  subject,  and  gives 
a  few  suggestions  that  should  be  heeded  carefully. 

Forest  Fires 

The  great  annual  destruction  of  forests  by  fire  is  an  injury 
to  all  persons  and  industries.  The  welfare  of  every  community 
is  dependent  upon  a  cheap  and  plentiful  supply  of  timber,  and 
a  forest  cover  is  the  most  effective  means  of  preventing  floods 
and  maintaining  a  regular  flow  of  streams  used  for  irrigation 
and  other  useful  purposes. 

To  prevent  forest  fires  Congress  passed  the  law  approved 
May  5,  1900,  which  — 

Forbids  setting  fire  to  the  woods,  and 
Forbids  having  any  fires  unextinguished. 

This  law,  for  offenses  against  which  officers  of  the  Forest 
Service  can  arrest  without  warrant,  provides  as  a  maximum 
punishment  — 

A  fine  of  $5000,  or  imprisonment  for  two  years,  or  both,  if 
the  fire  is  set  maliciously,  and 

A  fine  of  $1000,  or  imprisonment  for  one  year,  or  both,  if 
fire  results  from  carelessness. 

It  also  provides  that  the  money  from  such  fines  shall  be 
paid  to  the  school  fund  of  the  county  in  which  the  offensr  i- 
committed. 

The  exercise  of  care  with  small  fires  is  the  best  preventive  of 
large  ones.  Therefore  all  persons  are  requested  — 


614  EVERYDAY   SCIENCE 

1.  Not  to  drop  matches  or  burning  tobacco  where  there  is 
inflammable  material. 

2.  Not  to  build  larger  camp  fires  than  are  necessary. 

3.  Not  to  build  fires  in  leaves,  rotten  wood,  or  other  places 
where  they  are  likely  to  spread. 

4.  In  windy  weather  and  in  dangerous  places,  to  dig  holes 
or  clear  the  ground  to  confine  camp  fires. 

The  fire  may  be  confined  in  various  ways.  A  circle  of  stones 
may  be  built  around  the  fire,  with  the  draft  provided  on  the  side 
away  from  the  windward.  Or,  a  pit  may  be  dug,  and  the  dirt  from 
the  pit  cast  up  in  a  semicircle  to  windward,  with  the  opposite  side 
more  shallow  to  provide  for  draft.  If  the  wind  is  high,  it  is  wise  to 
clear  a  space  of  fifteen  or  twenty  feet  in  diameter  by  removing  all 
inflammable  material  and  leaving  only  the  bare  earth  exposed.  Al- 
ways have  several  buckets  of  water  at  hand  to  be  used  in  case  of 
accident. 

5.  To  extinguish  all  fires  completely  before  leaving  them, 
even  for  a  short  absence. 

"A  fire  is  never  out,"  says  Chief  Forester  H.  S.  Graves,  "  until 
the  last  spark  is  extinguished.  Often  a  log  or  snag  will  smolder 
unnoticed  after  the  flames  have  apparently  been  conquered,  only 
to  break  out  afresh  with  a  rising  wind." 

To  prevent  the  re-kindling  of  a  fire  after  it  has  apparently  been 
extinguished,  pour  water  over  it  and  soak  all  the  ground  around 
within  a  radius  of  several  feet.  If  water  is  not  available,  cover  the 
charred  remains  of  the  fire  completely  with  earth. 

6.  Not  to  build  fires  against  large  or  hollow  logs,  where 
it  is  difficult  to  extinguish  them. 

7.  Not  to  build  fires  to  clear  land  without  informing  the 
nearest  officer  of  the  Forest  Service,  so  that  he  may  assist  in 
controlling  them. 

PROJECT  XXXVIII.  —  Garden  Projects,  pages  366-399 

In  a  manual  of  this  sort,  it  is  not  practicable  to  offer  any  single 
garden  project,  since  weather  and  soil  conditions  differ  so  widely 


PROJECTS  615 

in  various  regions.  Soil  conditions  may  vary  greatly  even  in  the 
same  community. 

Among  the  best  pamphlets  on  flower,  fruit,  and  vegetable  gar- 
dening are  those  issued  by  certain  wholesale  dealers  in  seeds  and 
by  the  United  States  Department  of  Agriculture.  A  number  of 
books  are  listed  below,  with  comments  as  to  their  nature  and  degree 
of  usefulness  for  beginners. 

Vegetables. —  "Home  Vegetable  Gardening,"  F.  F.  Rockwell. 
J.  C.  Winston  Co.,  1911. 

"The  Home  Garden,"  Eben  E.  Rexford.  J.  B.  Lippincott  Co., 
1909.  These  two  books  are  very  good  guides  for  the  amateur. 
They  deal  with  vegetable  gardening  and  fruit  gardening,  furnish 
useful  hints  as  to  the  general  planning  of  gardens. 

"The  Home  Vegetable  Garden,"  Adolph  Kruhm.  Orange  Judd 
Co.  Treats  of  each  vegetable  separately.  Designed  for  the  eastern 
section  of  the  United  States. 

"Home  Vegetable  Gardening  from  A  to  Z,"  Adolph  Kruhm. 
Doubleday,  Page  and  Co.,  1918.  The  same  type  of  book  as  the 
preceding,  but  written  with  special  reference  to  Pacific  Coast  con- 
ditions. 

"Farm  Friends  and  Foes,"  C.  M.  Weed.     D.  C.  Heath  &  Co. 

"Home  Gardening  in  the  South,"  Farmers'  Bulletin  No.  934, 
United  States  Department  of  Agriculture. 

"The  Farm  Garden  in  the  North,"  Farmers'  Bulletin  No. 
937. 

"The  City  and  Suburban  Vegetable  Garden,"  Farmers'  Bulletin 
No.  936. 

"Control  of  Diseases  and  Insect  Enemies  of  the  Home  Vegetable 
Garden,"  Farmers'  Bulletin  No.  856. 

"Home  Storage  of  Vegetables,"  Farmers'  Bulletin  No.  879. 

Fruits, —  "Growing  Fruit  for  Home  Use,".  Farmers'  Bulletin 
No.  1001. 

"Making  a  Garden  of  Small  Fruits,"  F.  F.  Rockwell.  McBride, 
Nast  &  Co.,  1914. 

"Home  Vegetable  Gardening  "  (Part  III),  F.  F.  Rockwell.  J.  C. 
Winston  Co.,  1911. 


616  EVERYDAY  SCIENCE 

"The  Home  Garden  "  (Chapters  XIV  to  XVII),  Eben  E.  Rex- 
ford.  J.  B.  Lippincott  Co.,  1909. 

Flowers.  —  "  A-B-C  of  Gardening,"  Eben  E.  Rexford.  Harper  and 
Bros.,  1915.  A  very  simple  and  useful  book  on  flower  culture. 

"Yard  and  Garden,"  Tarkington  Baker.  Bobbs-Merrill  Co., 
1908.  On  the  care  of  lawn,  flowers,  vines,  shrubs,  and  trees.  A 
good  all-around  book  for  the  amateur. 

"Manual  of  Gardening,"  L.  H.  Bailey.  Macmillan  Co.,  1911. 
A  larger  book  than  either  of  the  two  preceding.  It  treats  of  the 
care  of  the  lawn,  ornamental  plants,  shrubs,  and  trees,  and  devotes 
a  chapter  each  to  the  growing  of  small  fruits  and  of  vegetables. 

PROJECT  XXXIX.  —  How   to   Raise   Strawberries   without   Garden 
Space,  pages  366-399 

It  frequently  happens  in  crowded  sections  of  cities  that  there  is 
no  space  in  yards  or  near-by  vacant  lots  for  any  kind  of  gardening. 
It  is  interesting  and  profitable,  therefore,  to  see  what  can  be  done 
with  a  flour-barrel  —  or  any  other  tightly  constructed  barrel  — 
filled  with  rich,  loamy  soil,  and  placed  on  a  sunlit  balcony  or  in  a 
sunny  corner  of  a  paved  court. 

After  the  barrel  has  been  filled  with  good  rich  soil  thoroughly 
mixed  with  well-rotted  manure,  draw  circles  about  the  barrel  par- 
allel to  the  top  and  about  six  inches  apart,  beginning  with  a  circle 
six  inches  below  the  mouth  of  the  barrel.  On  the  lines  of  these 
circles  bore  one-inch  holes  in  the  barrel,  six  inches  apart.  The  holes 
of  each  succeeding  circle  should  be  bored  just  below  the  middle  of 
the  spaces  in  the  circle  above. 

In  the  soil  on  top  and  in  the  holes  bored  through  the  sides  set 
strawberry  plants.  The  suggested  arrangement  of  holes  gives  the 
maximum  of  light  and  air  to  each  of  the  plants  growing  from  the 
holes.  Two  such  barrels  can  be  made  to  supply  a  good  sized  family 
with  strawberries  in  season. 

Remember  to  keep  the  barrel  where  it  can  get  the  sunlight  and 
be  sure  to  keep  it  watered.  Be  sure  not  to  keep  it  drenched.  If 
water  keeps  running  through  the  soil  in  too  great  abundance  and 


PROJECTS  617 

draining  from  the  hole  and  from  the  bottom  of  the  barrel,  it  will 
not  only  wash  the  loam  from  the  holes  and  expose  the  roots  of  plants, 
but  will  also  wash  the  fertility  out  of  the  soil. 

For  careful  instructions  as  to  how  to  raise  strawberries,  write  the 
United  States  Department  of  Agriculture  for  a  copy  of  Farmers' 
Bulletin  No.  198. 

PROJECT  XL.  —  How  to  Irrigate  a  Smatt  Garden,  pages  366-399 
Inexperienced  gardeners  frequently  make  the  mistake,  in  dry 
weather,  of  sprinkling  the  surface  of  the  soil  lightly  and  frequently. 
This  surface  supply  of  water  quickly  evaporates.  Moreover,  this 
method  of  watering  tends  to  lure  the  roots  toward  the  surface  in- 
stead of  making  them  strike  deep,  as  the  roots  of  hardy  plants 
should  strike,  into  the  soil.  It  is  better,  either  with  garden  or 
lawn,  to  soak  a  portion  of  it  at  a  time,  possibly  taking  several  days 
to  cover  the  whole  plot,  rather  than  to  sprinkle  the  surface  lightly 
every  day. 

Where  one  does  not  enjoy  the  convenience  of  an  unlimited  water- 
supply  and  a  garden  hose,  but  has  to  carry  water  in  bucket-  ti> 
the  garden,  a  very  satisfactory  system  of  irrigation  on  a  small 
plot  of  ground  can  be  established  with  the  aid  of  large  cans  and 
buckets  taken  from  the  tin  can  pile.  Take  one-half  gallon  or  gal- 
lon cans  or  even  old  galvanized  iron  buckets.  Perforate  the  sides 
with  a  hammer  and  a  ten-penny  nail.  Sink  the  cans  to  the  level 
of  the  ground,  about  two  or  three  feet  apart,  between  rows  of  gar- 
den stuff. 

Fill  the  cans  with  water  instead  of  sprinkling  the  surface  of  the 
soil.  A  gallon  of  water  furnished  directly  to  the  roots  of  plants  in 
this  way  will  do  more  good  than  three  gallons  applied  to  the  surface 
of  the  soil. 

PROJECT  XLL  —  How  to  Cold-pack  a  Vegetable—  Tomatoes,  page  440 
Start  with  clean  hands,  clean  utensils,  and  pure  clean  water. 
Use  only  clean,  sound  fresh  tomatoes.     No  fruit  or  vegetable 
which  is  withered  or  unsound  should  ever  be  cold-packed.     If 
possible,  use  only  vegetables  picked  on  the  day  of  canning. 


618  EVERYDAY   SCIENCE 

Glass  jars  are  much  to  be  preferred  to  metal  cans  for  home  canning. 
Soft,  elastic  rubbers  of  the  best  grade  should  be  used.  Never  use 
old  or  cheap  rubbers.  The  best  are  the  most  economical. 

After  washing  and  rinsing  the  jars  carefully,  submerge  them  in 
a  vessel  of  cold  water.  Submerge  the  lids  and  rubbers  hi  cold  water 
in  a  separate  vessel.  Heat  the  water  in  these  vessels  slowly  and 
allow  it  to  boil  for  fifteen  minutes.  Allow  the  jars,  rubbers,  and 
covers  to  remain  in  the  hot  water  until  you  are  ready  to  use  them. 
Do  not  touch  the  insides  of  jars  or  covers  with  your  fingers  in  the 
process  of  packing.  Sterilize  in  the  same  way  all  spoons,  cups,  and 
other  utensils  used  for  packing  the  tomatoes. 

Wash  the  tomatoes  carefully  hi  cold  water. 

Place  them  in  a  cheesecloth  bag  or  dipping  basket,  and  dip  them 
in  boiling  water.  Allow  them  to  remain  for  1^  minutes.  A  shorter 
period  of  scalding  may  loosen  the  skins ;  but  unless  sufficient  time 
is  given  for  scalding,  the  tomatoes  may  shrink  after  packing. 

Lift  the  bag  or  basket  of  tomatoes  from  the  boiling  water  and 
plunge  them  into  cold  water. 

Slip  off  the  skins ;  and  if  you  wish,  remove  the  cores  of  the  larger 
tomatoes,  though  the  removal  of  cores  is  not  necessary. 

Pack  the  tomatoes  directly  into  the  sterilized  jars.  Press  them 
down  with  a  sterilized  silver  tablespoon,  but  do  not  crush  them. 
Do  not  add  water.  The  jar  may  be  filled,  however,  with  the  juice 
of  the  soft  or  broken  tomatoes. 

Add  a  level  teaspoonful  of  salt  for  each  quart  of  tomatoes. 

Now  adjust  the  rubbers  and  covers  but  do  not  seal  them.  In  the 
case  of  jars  of  the  Ball-Mason  type,  screw  the  cover  on  only  as  far 
as  you  can  easily  screw  it  with  your  thumb  and  little  finger.  In 
the  case  of  jars  of  the  "Economy"  or  vacuum  sealing  type,  place 
the  cover  on  and  clamp  it  down  with  the  spring.  In  the  case  of 
clamp  top  jars,  put  on  the  cover,  lift  the  wire  into  place,  but  do 
not  shut  down  the  clamp.  This  is  to  allow  for  the  escape  of  steam 
and  expanded  air  during  the  process  of  sterilization. 

Place  in  a  clean  wash  boiler  a  false  bottom  of  wood  or  metal 
grating  in  order  to  keep  the  jars  off  the  bottom  of  the  boiler.  Better 
than  this,  wire  cages  may  be  bought  at  very  moderate  expense, 


PROJECTS  619 

which  serve  to  keep  the  jars  off  the  bottom  of  the  boiler  and  furnish 
handles  for  removing  the  jars  from  the  boiling  water  at  the  end  of 
the  process  of  sterilization. 

Put  cold  or  tepid  water  into  the  boiler  to  the  depth  of  two  or 
three  inches  and  place  the  boiler  over  the  flame.  Place  the  jars  in 
the  boiler,  and  add  enough  cold  or  tepid  water  to  cover  the  jars  to 
a  depth  of  several  inches,  but  not  enough  to  allow  the  boiling  water 
to  reach  the  covers  of  the  jars. 

Cover  the  boiler  and  allow  the  jars  to  remain  in  it  for  22  minutes 
after  the  water  begins  to  boil. 

At  the  end  of  22  minutes  of  sterilization,  remove  the  boiler  from 
over  the  fire,  take  the  jars  out  immediately,  and  tighten  the  covers. 
The  clamp-type  or  the  Ball-Mason  jars  may  be  inverted  a  few 
minutes  to  test  for  leakage.  The  vacuum  seal  jars  should  not  be 
inverted.  Let  them  stand  until  they  are  cool.  If,  when  the  jars 
are  cool,  you  can  lift  them  from  the  table  by  holding  to  the  covers 
alone,  they  are  probably  free  of  leakage. 

For  information  as  to  cold-packing  other  vegetables  and  as  to 
varying  the  time  of  sterilization  for  altitudes  higher  than  1000 
feet  above  sea-level,  write  to  the  United  States  Department  of 
Agriculture  for  a  copy  of  Fanners'  Bulletin  No.  839,  "  Home  Canning 
by  the  One-period  Cold-pack  Method."* 

For  canning  by  the  cold-pack  method  in  high  altitudes,  the 
pressure  cooker  is  very  desirable.  The  increased  temperature 
makes  sterilization  more  certain  and  hastens  the  process. 

PROJECT  XLII.  —  How  to  Cold-pack  Certain  Berries  with  Sugar, 
page  440 

The  following  particular  instructions  apply  to  the  cold-packing 
of  blackberries,  blueberries,  currants,  dewberries,  black  raspberries, 
and  huckleberries,  but  not  strawberries,  red  raspberries,  or  goose- 
berries. For  cold-packing  other  kinds  of  fruits,  see  Farmers' 
Bulletin  No.  839,  United  States  Department  of  Agriculture. 

Sterilize  jars,  covers,  rubbers,  and  all  utensils,  as  directed  for 
cold-packing  tomatoes  (Project  XLI). 


620  EVERYDAY  SCIENCE 

If  possible,  obtain  berries  picked  on  the  day  of  canning.  Cull, 
stem,  and  place  them  in  a  clean  strainer. 

Prepare  a  medium  thin  sirup  as  follows :  Into  3  quarts  of  cold 
water  put  two  quarts  of  sugar.  When  the  water  has  boiled  just 
enough  to  dissolve  all  the  sugar  thoroughly  but  not  enough  to  make 
the  solution  sticky,  you  have  a  thin  sirup.  To  make  a  medium  thin 
sirup,  continue  to  boil  until  the  solution  begins  to  thicken  and 
becomes  sticky  when  cooled  on  the  finger  tip  or  on  a  spoon. 

Rinse  the  berries  in  the  strainer  by  pouring  cold  water  over  them. 

Pack  directly  from  the  strainer  into  hot  jars  with  a  spoon  or  ladle. 
Do  not  crush  the  fruit. 

Pour  the  hot  sirup  over  the  fruit  until  the  jar  is  level  full  and 
ready  to  overflow. 

Place  the  rubbers  and  covers  in  position  without  sealing. 

N.  B.  Pack  each  jar,  cover  the  fruit  in  it  with  hot  sirup,  and  adjust 
the  covers  and  rubbers,  before  you  begin  to  pack  the  next  jar. 

The  operation  of  sterilizing  the  packed  fruit  is  exactly  the  same 
as  in  sterilizing  the  packed  tomatoes,  except  that  the  berries  need 
be  left  in  the  boiler  only  16  minutes  after  the  water  has  begun  to  boil. 

Remove  from  the  boiler,  tighten  the  covers,  and  test  for  leakage. 

Store  in  a  dark  closet  to  prevent  bleaching.  If  you  have  no  dark 
closet,  wrap  the  jars  in  newspapers. 

PROJECT  XLIII.  —  How  to  Cold-pack  Fruit  without  Sit  gar,  page  440 

Many^  excellent  housekeepers  maintain  that  the  flavor  of  the 
fresh  fruit  is  retained  better  by  canning  without  sugar.  In  such 
case,  the  sugar  is  added  just  before  serving.  For  pie  filling  or  salad 
purposes,  fruit  cold-packed  without  sugar  is  superior  to  that  cold- 
packed  in  sirup. 

It  is  almost  essential,  in  canning  fruit  without  sugar,  that  the 
fruit  be  picked  on  the  day  of  canning.  Cull  the  fruit,  stem,  seed, 
or  core  it,  and  clean  it  by  placing  it  in  a  strainer  and  pouring  cold 
water  over  it. 

The  process  of  cold-packing  without  sugar  differs  from  the  process 
of  cold-packing  with  sugar  only  in  two  essentials  : 


PROJECTS  621 

1.  After  the  fruit  has  been  packed  into  the  jars,  pour  boiling 
water,  instead  of  hot  sirup,  over  the  fruit  until  the  jar  overflows. 

2.  Leave  the  packed  fruit  in  the  boiler  for  30  minutes  after  the 
water  has  begun  to  boil. 

PROJECT  XLIV.  —  How  to  Preserve  Vegetables  and  Fruit  by  Drying, 
page  440 

For  some  city  dwellers  cold-packing  is  much  to  be  preferred  to 
the  process  of  drying.  Unless  you  have  an  oversupply  of  vege- 
tables and  fruits  in  your  own  garden,  and  can  thus  obtain  them 
absolutely  fresh  and  without  extra  cost,  you  will  probably  find  it 
neither  economical  nor  satisfactory  in  other  ways  to  experiment 
with  the  drying  of  vegetables. 

If,  on  the  other  hand,  you  have  an  oversupply  of  vegetables 
in  your  own  garden  that  you  cannot  sell,  and  you  have  no  jars  for 
cold-packing,  by  all  means  dry  your  vegetables  and  fruits  for  winter 
use  or  for  winter  markets.  Many  people  much  prefer  the  flavor 
of  certain  dried  fruits  and  vegetables  to  that  of  corresponding 
canned  products. 

It  is  hardly  profitable  to  undertake  the  drying  of  a  fruit  or  vege- 
table simply  to  satisfy  one's  curiosty.  If,  on  the  other  hand,  an 
oversupply  of  garden  produce  makes  drying  a  practical  and 
economical  project,  detailed  instructions  are  needed  for  guidance. 
Such  instructions,  differing  for  each  vegetable  and  fruit,  are  given 
in  Farmers'  Bulletin  No.  984,  "Farm  and  Home  Drying  of  Fruits 
and  Vegetables,"  United  States  Department  of  Agriculture. 

PROJECT  XLV.  —  How  to  Store  Eggs  for  Winter  Use, 
page  440 

Eggs  are  most  abundant  and  cheapest  in  spring  and  early  summer. 
This  is  the  time  to  store  them  for  winter  use.  To  obtain  the  most 
satisfactory  resists,  do  not  store  any  but  perfectly  fresh  eggs. 
Eggs  are  somewhat  like  milk;  they  get  their  taint  not  so  much 
from  being  in  storage  as  from  careless  handling  before  they  are 


622  EVERYDAY  SCIENCE 

stored.     They  should  be  kept  away  from  all  musty  odors  and  in 
a  cool  place  from  the  time  they  are  laid  until  they  are  eaten. 

The  three  successful  methods  of  preserving  eggs,  aside  from  cold 
storage,  are  to  varnish  them  with  vaseline,  to  submerge  them  in 
lime  water,  and  to  submerge  them  in  a  solution  of  water  glass. 
Of  these  three  methods,  the  water  glass  solution  is  the  most  satis- 
factory. It  must  not  be  expected  that  preserved  eggs  will  be  as 
palatable  as  fresh  eggs,  but  if  they  are  packed  fresh  in  a  solution 
of  water  glass  that  is  not  too  alkaline,  they  will  compare  very 
favorably  with  the  eggs  that  are  bought  at  your  grocer's  in  winter. 
For  cooking  purposes  they  are  just  as  satisfactory  as  fresh  eggs. 

Water  glass  may  be  bought  as  a  thick  sirup.  It  should  be  used 
in  the  proportions  of  1  volume  of  water  glass  to  10  volumes  of 
water.  Water  glass  that  is  too  strongly  alkaline  will  make  eggs 
bitter. 

To  Preserve  10  Dozen  Eggs.  —  Boil  5  quarts  of  water  and  allow 
it  to  cool.  Add  one  pint  of  water  glass.  Put  the  solution  in 
earthenware  crocks  or  wooden  pails  that  can  be  covered  tightly. 
Be  sure  that  the  receptacles  are  clean  and  odorless,  and  be  sure 
that  the  eggs  are  wiped,  but  not  washed,  clean  before  putting  them 
in  the  solution.  (Washing  removes  an  outer  protective  coating 
from  the  eggshell.)  After  the  eggs  have  been  put  in  the  solution, 
small  end  down,  cover  the  receptacle  and  put  it  in  a  cool  place. 

If  you  boil  eggs  that  have  been  preserved  in  water  glass,  run 
a  needle  through  the  shell  at  the  large  end.  This  will  prevent  the 
shell  from  breaking  through  expansion  of  the  moisture  and  air  inside. 

PROJECT  XLVI.  —  How  to  Distinguish  Fresh  from  Stale  Eggs, 
page  440 

(a)  Fresh  eggs  have  a  slightly  rough  coating  over  the  shell. 

(6)  Since  an  eggshell  is  porous,  an  egg  loses  in  time  part  of  its 
liquid  contents  by  evaporation.  This  causes  the  white  and  yolk 
to  shrink,  and  the  emptied  space  to  be  filled  withjar  or  some  other 
gas.  This  air  space  is  generally  at  the  broad  end  of  the  egg,  and 
in  a  good  egg  should  not  be  larger  than  a  dime. 


PROJECTS  623 

To  Test  Eggs  by  Candling.  —  Roll  a  sheet  of  cardboard  into  a  tube 
or  cylinder,  large  enough  to  fit  down  over  a  lamp  chimney  or 
a  candle.  A  large  shoe  box  with  the  ends  removed  and  the  cover 
fastened  in  place  will  serve  as  well.  In  the  side  of  the  tube  or  box 
opposite  the  flame,  cut  a  hole  somewhat  smaller  in  diameter  than  an 
ordinary  egg. 

Place  the  tube  over  a  candle,  lamp,  or  incandescent  lamp,  so  that 
the  light  is  visible  through  the  hole  in  the  side  of  the  tube.  Hold 
each  egg  to  the  opening  in  the  cardboard,  broad  end  up,  and  observe 
it  against  the  light.  In  a  good  fresh  egg,  the  air  space  is  small, 
the  yolk  appears  clear  and  round  in  dim  outline,  and  the  white  is 
clear.  If  the  air  space  is  rather  large  and  the  yolk  is  darkened,  the 
egg  is  stale.  If  the  contents  of  the  egg  appear  dark  or  hazy,  with 
a  black  spot,  the  egg  is  unfit  for  food. 

If  one  has  much  testing  of  this  kind  to  do,  it  is  better  to  secure 
a  candling  chimney  for  a  small  sum  at  a  poultry  store. 

(c)  The  loss  of  liquid  content  by  evaporation  makes  an  egg  lighter, 
and  so  it  may  be  tested  by  its  specific  density  (p.  150).  Make  a 
solution  of  one  quart  of  water  with  two  tablespoonfuls  of  salt. 
A  fresh  egg  will  sink  in  this  solution.  A  very  stale  egg  will  float. 
Eggs  at  stages  between  a  very  fresh  and  a  very  stale  egg  may  float 
at  various  depths. 

PROJECT  XLVII.  —  How  to  Dress  a  Minor  Wound, 
pages  444-445 

No  home,  office,  or  school  should  be  without  a  Red  Cross  First 
Aid  Kit. 

Do  not  attempt  home  treatment  for  anything  but  scratches  or 
shallow  cuts  or  punctures.  In  case  of  deep  cuts,  accompanied  by 
severe  bleeding,  call  a  doctor  immediately.  Pressure  on  the  wound 
with  a  pad  of  aseptic  gauze  will  retard  the  flow  of  blood  until  the 
doctor  can  arrive.  Do  not  use  your  fingers  or  an  unclean  cloth  for 
this  purpose.  ^ 

If  the  blood  comes  in  spurts,  an  artery  has  been  cut.  In  this 
event,  pressure  should  be  exerted,  if  possible,  on  the  supply  artery 


624  EVERYDAY  SCIENCE 

between  the  wound  and  the  heart.  The  artery  can  often  be  located 
by  its  pulsations.  In  case  of  a  severed  artery  in  leg  or  arm,  let  the 
patient  lie  on  his  back  and  elevate  the  wounded  leg  or  arm.  An 
elastic  band,  a  pair  of  elastic  suspenders,  or  a  tightly  wrapped 
bandage  applied  between  the  wound  and  the  heart  will  often  serve 
to  stop  the  bleeding  in  15  or  20  minutes. 

In  very  severe  cases,  a  tourniquet  may  be  used.  To  make 
a  tourniquet,  knot  a  strong  handkerchief  or  cloth  about  the  arm 
or  leg  above  the  wound,  place  the  knot  over  the  supply  artery, 
and  use  a  stick  to  twist  the  bandage  as  tight  as  necessary.  Such 
a  bandage  should  not  be  left  on  more  than  20  minutes.  If  the 
doctor  has  not  arrived  in  that  time,  exert  pressure  with  a  pad  over 
the  wound  itself  for  about  five  minutes  and  then  replace  the  tour- 
niquet. 

In  case  of  deep  punctures,  such  as  are  made  by  nails,  long  splinters, 
etc.,  have  them  cleaned  and  disinfected  immediately  by  a  doctor 
to  avoid  danger  of  lockjaw  or  blood  poisoning. 

Never  neglect  minor  incisions,  scratches,  or  punctures.  See 
first  that  ah1  foreign  matter  is  removed  from  the  wound  and  from 
the  surface  around  it.  This  should  be  done  with  a  piece  of  aseptic 
gauze  and  carbolic  acid  solution  (1  teaspoonful  of  carbolic  acid  or 
lysol  to  a  pint  of  water),  boric  acid,  bichloride  of  mercury  solution, 
turpentine,  or  grain  alcohol.  See  that  the  antiseptic  solution 
reaches  every  part  of  the  wound. 

If  there  is  tendency  to  bleeding,  bandage  the  wound  firmly  with 
aseptic  gauze.  A  bandage  is  also  useful  to  keep  the  wound  from 
coming  in  contact  with  infected  surfaces.  If  the  wound  is  where 
there  is  little  if  any  danger  of  such  infection  by  contact,  do  not  be 
afraid  to  leave  it  open  to  light  and  air.  This  is  infinitely  better 
anyhow  than  binding  it  with  a  cloth  that  is  not  clean  or  closing  it 
up  with  unclean  court  plaster. 

Quick  closing  of  the  surface  of  a  wound  is  not  desirable.  The 
healing  should  be  "from  the  inside  out."  If  inflammation  and 
soreness  persist,  it  will  frequently  be  found  that  the  wound  needs 
to  be  reopened  with  a  sharp  instrument  that  has  been  disinfected 
by  dipping  it  in  alcohol  or  carbolic  acid.  When  the  wound  has 


PROJECTS  625 

been  opened,  cleanse  it  again  with  carbolic  acid  solution,  bichloride 
of  mercury  solution,  turpentine,  or  grain  alcohol. 

Do  not  attempt  to  reopen  or  cleanse  deep  wounds.  That  is 
a  doctor's  work. 

Caution.  —  Do  not  depend  on  ordinary  peroxide  of  hydrogen  for 
disinfecting. 

Two  of  the  best  and  simplest  books  on  first  aid  are : 
"  First  Aid  for  Boys,"  Cole  and  Ernst.    D.  Appleton  &  Co. 
"American   Red    Cross   Abridged   T*jxt-Book   on   First   Aid," 
P.  Blakiston's  Son  &  Co. 

PROJECT  XL VIII.  —  How  to  Disinfect  a  Room  by  Fumigation, 
pages  444-445 

The  most  important  thing  to  be  done  at  the  outset  is  to  seal  the 
room  thoroughly  so  as  to  prevent  the  escape  of  gas  until  the  process 
of  fumigation  is  completed.  Close  all  windows  and  doors,  except 
the  door  provided  for  exit,  but  leave  the  windows  unlocked  so  that 
they  may  be  opened  from  the  outside.  The  temperature  of  the 
room  should  be  at  least  60°  F.  or  higher.  The  higher  the  tem- 
perature the  better,  provided  there  is  no  exposed  flame  in  the 
room. 

Make  a  formaldehyde  solution  by  dissolving  12  ounces  of  40% 
solution  of  formaldehyde  in  1  gallon  of  water.  Soak  strips  of  paper 
in  this  solution  and  paste  4  to  6  thicknesses  of  them  with  paper- 
hanger's  paste  over  all  door,  transom,  and  window  cracks,  over 
stove-holes,  keyholes,  registers,  or  any  other  openings  of  any  sort. 
After  the  strips  are  in  place,  wet  them  thoroughly  with  a  brush 
dipped  in  the  paste.  Large  openings  may  need  more  than  a  single 
thickness  of  paper.  To  prevent  the  skin  of  the  hands  from  roughen- 
ing or  peeling,  grease  the  hands  or  put  on  rubber  gloves  before 
handling  the  formaldehyde  solution.  The  fumes  from  this  small 
amount  of  the  solution  may  be  disagreeable  but  they  are  not 
dangerous. 

Hang  clothing,  bed  covers,  and  everything  that  cannot  be  dis- 
infected by  boiling,  on  lines  stretched  across  the  room.  Stretch 


626  EVERYDAY  SCIENCE 

shades  and  curtains  to  full  length.  Open  long  seams  on  pillows 
and  mattresses  and  set  them  on  edge.  Open  closet  doors,  dresser 
drawers,  chests,  and  trunks.  Open  books  and  spread  them  out. 
In  short,  make  it  possible  for  the  fumes  to  reach  every  part  of 
everything  in  the  room. 

Now  place  an  ordinary  wood  or  fiber  washtub  in  the  center  of 
the  room.  In  the  middle  of  the  tub  put  two  bricks  on  edge  as 
a  base  for  a  large  bucket. 

Before  proceeding  to  fumigate,  moisten  the  air  of  the  room 
thoroughly  by  boiling  water  hi  the  room,  by  dropping  hot  bricks 
into  warm  water,  or  by  using  an  atomizer.  The  first  method  is 
the  most  effective.  Remember  that  a  moist  atmosphere  is  essential 
to  effective  fumigation.  The  cloudier  the  room  becomes  with 
moisture  the  better. 

When  the  room  is  ready,  spread  10  ounces  of  potassium  per- 
manganate (the  needle-like  crystals,  not  the  rhomboid  crystals 
nor  the  dust)  evenly  over  the  bottom  of  a  14-quart  bucket  having 
rolled,  not  soldered,  seams.  Put  enough  boiling  water  into  the  tub 
to  reach  almost  but  not  quite  to  the  top  of  the  bricks.  Put  the 
bucket  on  the  bricks  in  the  center  of  the  tub.  Pour  into  the  bucket 
24  ounces  of  formaldehyde  solution.  The  reaction  between  the 
potassium  permanganate  and  the  formaldehyde  solution  is  very 
rapid  and  formaldehyde  is  liberated  in  great  quantities.  Be  sure, 
therefore,  that  everything  is  in  readiness  for  you  to  beat  a  hasty 
retreat  and  to  seal  the  door  of  exit,  before  you  pour  in  the  formalde- 
hyde solution.  Leave  the  room  sealed  for  six  hours. 

Be  careful  in  handling  the  potassium  permanganate.  It  is  likely 
to  stain  anything  with  which  it  comes  in  contact.  The  effervescent 
action  is  so  violent  when  the  formaldehyde  solution  is  poured  on 
the  potassium  permanganate  that  the  bucket  must  be  fully  as  large 
as  indicated.  If  convenient,  have  it  larger. 

The  amount  of  chemicals  indicated  is  sufficient  to  fumigate 
a  room  12X12X10.  If  the  room  is  larger,  provide  more  tubs  and 
buckets.  Do  not  increase  the  amount  of  the  chemicals  for 
a  single  bucket.  This  process  can  be  depended  upon.  Not  all 
the  fumigating  candles  and  advertised  apparatus  are  so  reliable. 


PROJECTS  627 

Even  if  candles  approved  by  health  authorities  are  used,  it  is  best 
to  use  twice  as  taany  of  them  as  directed. 

Fumigating  with  Sulphur  Candles.  —  The  preparation  of  the  room 
for  fumigation  is  exactly  the  same  as  for  fumigating  with  formalde- 
hyde. For  a  room  12X12X10,  six  of  the  pound  candles  would  be 
needed,  no  matter  what  the  directions  accompanying  the  candles 
may  call  for.  Put  them  in  pans  on  the  table,  not  on  the  floor,  in 
the  center  of  the  room,  fill  the  water  jackets  two  thirds  full,  light 
the  candles,  leave  the  room  promptly,  and  seal  the  exit  door.  Leave 
the  room  sealed  for  from  12  to  24  hours. 

The  advantage  of  sulphur  fumigation  over  formaldehyde  fumiga- 
tion is  that  it  kills  all  insects  as  well  as  germs  and  thus  prevents 
insects  carrying  the  disease. 

The  disadvantage  is  that  the  fumes  of  sulphur  tend  to  bleach 
and  otherwise  to  impair  all  kinds  of  fabrics,  and  are  apt  to  injure 
brass,  copper,  steel,  or  gilt  work. 

NOTE.  —  An  excellent  gum  for  use  in  sealing  the  room  with  news- 
paper strips  is  powdered  gum  tragacanth.  Soak  two  teaspoonfuls 
of  powdered  gum  tragacanth  in  one  pint  of  cold  water  for  an  hour. 
Then  place  the  vessel  containing  the  mixture  in  a  pan  of  boiling  water 
and  stir  until  the  gum  is  dissolved.  This  seals  effectively,  washes  off 
easily,  and  will  not  stain  or  discolor  woodwork  at  all. 

PROJECT  XLIX.  —  How  to  Prevent  Dampness  in  Cellars  and 
Dark  Closets,  page  444 

Since  dampness  and  darkness  are  favorable  to  the  growth  of 
bacteria  and  molds,  and  furnish  inviting  conditions  for  waterbugs, 
roaches,  and  other  disagreeable  insects,  modern  houses  are  built 
as  nearly  damp-proof  and  as  free  from  dark  corners  as  possible. 
In  many  old-fashioned  or  ill-constructed  houses,  there  are  damp 
and  dark  closets  and  cellar-rooms.  To  the  unpleasantness  and 
unhealthfulness  of  such  corners  is  added  the  loss  occasioned  by 
rust  and  mildew. 

Permanent  removal  of  these  conditions  by  whatever  building 
alterations  are  necessary  is  the  most  satisfactory  remedy,  and 


628  EVERYDAY  SCIENCE 

in  the  end  it  is  the  most  economical.  But  if  you  do  not  own  the 
house,  or  for  some  other  reason  you  find  it  impracticable  to  make 
the  necessary  alterations,  conditions  may  be  greatly  improved  by 
a  simple  expedient. 

Place  one  or  more  earthenware  bowls  of  quicklime  in  the  closets 
or  cellar-rooms.  The  amount  of  quicklime  will  depend  on  the  size 
of  the  closet  or  room.  Quicklime  rapidly  absorbs  moisture  from 
the  air  (p.  141  of  this  book)  and  counteracts  stale  odors  common 
to  such  places.  This  drying  of  the  atmosphere  lessens  the 
danger  of  rust  and  mildew.  Moreover,  the  odor  of  quicklime 
apparently  repels  insects  and  mice  that  are  likely  to  congregate 
in  such  places. 

When  the  lime  becomes  air-slaked,  substitute  a  fresh  supply. 
Do  not  throw  the  air-slaked  lime  away ;  you  may  find  it  useful 
for  your  lawn  or  garden  (p.  315  of  this  book ;  see  also  Project 
XXXVI). 

PROJECT  L.  —  How  to  Pasteurize  Milk  at  Home, 
pages  446-447 

Choose  a  covered  pail  large  enough  to  hold  the  bottle  or  jar  in 
which  the  milk  is  contained.  Obtain  a  pie  tin  that  just  about  fits 
inside  the  bottom  of  the  pail.  Perforate  the  pie  tin  and  place  it, 
inverted,  in  the  pail.  On  this  false  bottom  set  the  bottle,  or  bottles, 
of  milk,  tightly  capped  or  plugged  with  absorbent  cotton.  If  you 
buy  your  milk  in  bulk  rather  than  in  bottle  put  it  in  a  Ball-Mason 
jar,  sterilized  as  for  canning  vegetables  (Project  XLI).  Adjust  the 
rubber,  screw  down  the  cap  tightly,  and  put  the  jar  into  the  pail. 
Fill  the  pail  with  water  enough  to  rise  to  the  neck  of  the  bottle  but 
not  to  reach  the  mouth  of  the  bottle.  The  water  should  be  as 
warm  as  possible  without  being  hot  enough  to  break  the  bottle. 

Now  cover  the  pail,  put  it  on  the  stove,  and  bring  the  water  to 
a  boil.  The  minute  the  water  begins  to  boil,  not  simmer,  remove 
the  pail  and  its  contents  from  the  stove,  set  it  in  a  place  where 
it  will  not  lose  heat  rapidly,  and  cover  it  with  a  heavy  cloth.  Let 
it  so  remain  for  thirty  minutes.  Then  remove  the  milk  bottle  from 


PROJECTS  629 

the  pail  and  cool  it  as  rapidly  as  possible  without  breaking  the 
bottle.  All  possible  speed  in  cooling  the  bottle  is  just  as  important 
as  the  preliminary  heating.  As  soon  as  the  bottle  is  cool  enough, 
put  it,  still  tightly  capped,  into  the  refrigerator. 

In  pasteurizing  milk,  it  is  well  to  raise  its  temperature  to  150° 
F.  in  order  to  destroy  the  dangerous  bacteria,  but  not  to  exceed 
160°  so  as  to  avoid  scalding  or  boiling  the  milk.  The  method  out- 
lined above  accomplishes  this  as  well  as  it  can  be  accomplished 
without  special  apparatus.  It  might  be  supposed  that  more 
accurate  results  could  be  had  by  inserting  a  chemical  thermometer 
in  the  milk  itself  to  test  the  temperature  during  the  process  of 
sterilization. 

But  the  best  authorities  do  not  recommend  this  procedure  for 
home  pasteurization,  because  the  hole  for  the  insertion  of  the  ther- 
mometer prevents  perfect  sealing  of  the  milk  during  pasteurization 
and  makes  contamination  possible  through  careless  handling  after- 
wards. It  must  be  remembered  that  pasteurization  kills  the 
bacteria  in  milk,  but  it  does  not  eliminate  dirt  or  prevent  milk 
from  being  contaminated  afterward  through  carelessness.  It  is 
important  that  places  where  milk  is  kept  should  be  spotlessly  clean ; 
refrigerators  especially  should  be  looked  after  in  this  regard. 

Where  milk  is  to  be  pasteurized  regularly  for  infants,  a  home 
should  be  provided  with  one  of  the  commercial  pasteurizers,  such 
as  the  Freeman  or  the  Straus  Home  Pasteurizer.  In  these  the  milk 
may  be  subjected  to  exactly  the  right  temperature  for  the  correct 
length  of  time,  and  then  cooled  quickly.  Moreover,  the  milk  may 
be  pasteurized  in  the  bottles  from  which  the  infant  takes  it.  The 
Straus  Home  Pasteurizer,  invented  by  Nathan  Straus,  the  great 
crusader  for  pure,  clean  milk,  is  inexpensive,  easy  to  manipulate,  and 
"  fool-proof."  Instructions  for  making  and  using  such  a  pasteurizer, 
if  one  cannot  be  bought  in  your  community,  are  given  in  the  fol- 
lowing books : 

"Disease  in  Milk;  the  Remedy  Pasteurization,"  Lina  G.  Straus. 
N.  Y.,  1913. 

"The  Milk  Question,"  M.  J.  Rosenau.  Houghton  Mifflin  Com- 
pany, 1912. 


630  EVERYDAY  SCIENCE 

PROJECT  LI.  —  How  to  Test  the  Home  Water-supply  for 
Organic  Impurities,  page  447 

(a)  In  a  clean  porcelain  dish  boil  one  quart  of  the  water  to  be 
tested.  Continue  to  boil  it  until  it  evaporates. 

If  what  remains  in  the  bottom  of  the  vessel  immediately  after  the 
water  is  evaporated  is  white  and  powdery,  there  are  probably  only 
harmless  mineral  substances  in  solution  in  the  water-supply. 

If  what  remains  immediately  after  the  water  is  evaporated  is 
partly  white  and  partly  yellowish  or  greenish,  with  gum-like  stains 
around  the  edge  of  the  residue,  the  water  contains  organic  impurities 
of  either  vegetable  or  animal  origin. 

Continue  to  heat  the  residue.  If  the  yellowish  or  greenish  or 
gum-like  portions  turn  black,  sputter,  and  burn  away,  giving  out 
an  offensive  smell  like  burning  feathers,  the  organic  matter  is  pretty 
certainly  of  animal  origin  and  is  unwholesome  if  not  positively 
poisonous. 

(6)  Unless  you  live  directly  on  the  seacoast  or  in  a  region  of 
salt-bearing  rocks,  neither  the  surface  nor  the  underground  water- 
supply  should  contain  more  than  a  minute  trace  of  common  salt. 
Anything  more  than  a  trace  of  common  salt  probably  has  its  origin 
in  vegetable  or  animal  refuse. 

To  Test  for  Salt.  —  To  a  tumblerful  of  the  water  to  be  tested,  add 
20  drops  of  nitric  acid,  and  a  small  crystal  of  nitrate  of  silver  —  or 
5  drops  of  a  solution  of  nitrate  of  silver.  Stir  with  a  clean  strip  of 
glass.  The  normal  amount  of  salt  will  be  indicated  by  a  faint 
bluish- white  cloudiness.  If  the  water  shows  marked  cloudiness 
or  a  solid  curdy  substance,  too  much  common  salt  is  present. 

The  presence  of  both  organic  matter  and  considerable  salt  in- 
dicates that  the  water  is  probably  contaminated  by  sewage  or 
stable  drainage.  The  source  of  pollution  should  be  discovered  and 
removed  without  delay.  In  the  meantime,  none  of  the  water 
should  be  used  for  drinking  or  cooking  without  purifying  it  since 
such  water  may  contain  bacteria  dangerous  to  the  health.  If 
there  is  the  slightest  doubt  about  the  fitness  of  water  for  drinking 
purposes,  it  should  be  treated  as  directed  in  Project  LII. 


PROJECTS  631 

PROJECT  LII.  —  How  to  Clarify  and  Purify  Water  for  Home 
Use,  page  448 

Water  may  be  murky  in  appearance  without  being  unwholesome ; 
on  the  other  hand  it  may  be  clear  without  being  pure.  But  clear 
water  is  at  least  inviting.  If  a  water-filter  is  used  to  clarify  water, 
it  should  be  thoroughly  cleansed  at  least  once  a  week  —  preferably 
oftener.  To  remove  heavy  sediment,  where  a  filter  is  not  used, 
water  may  be  strained  through  a  flannel  bag.  Small  flannel  bags 
with  running  strings  may  be  fastened  on  the  faucets.  These  should* 
be  changed  daily.  Wash  the  used  bags  with  soap  and  water  and 
hang  in  the  sun  to  dry. 

Water  that  contains  organic  substances  may  be  clarified  with  the 
use  of  alum.  The  alum  coagulates  albuminous  substances,  much 
as  boiling  coagulates  the  white  of  an  egg.  This  coagulated  albu- 
men settles  to  the  bottom  and  acts  like  a  net  in  carrying  down  other 
impurities  with  it. 

A  lump  of  alum  suspended  by  a  string  and  swung  about  in 
a  pitcher  for  a  minute  or  so  will  clarify  it. 

A  teaspoonful  of  powdered  alum  will  clarify  4  gallons  of  water. 
Stir  the  water  vigorously  before  adding  the  alum.  Allow  the 
impurities  to  settle  and  then  draw  the  water  in  such  a  way  as  not 
to  disturb  the  sediment.  The  alum,  if  there  is  not  too  much  used, 
will  settle  with  the  sediment. 

To  purify  contaminated  water,  boil  it  for  16  minutes.  This 
drives  off  the  air  and  makes  water  taste  flat.  To  restore  the 
sparkle,  pour  the  water  rapidly  from  one  vessel  to  another  several 
times.  This  aerates  the  water.  A  few  drops  of  lemon  juice  add 
surprisingly  to  the  palatability  of  boiled  water. 

PROJECT  LIII.  —  How  Boy  Scouts  Filter  and  Purify  Water 
for  Drinking,  page  448 

The  methods  applied  in  the  home  purification  of  water  may  be 
used  by  Boy  Scouts  in  field  or  camp.  Run  no  risks  whatever  with 
the  water  you  drink.  If  you  are  going  for  a  day's  tramp  and  are 


632  EVERYDAY  SCIENCE 

doubtful  of  the  purity  of  the  water  you  may  find,  take  a  canteen 
of  pure  water  with  you. 

Chlorine  is  the  substance  most  commonly  used  by  city  water 
departments  in  the  purification  of  contaminated  water-supplies. 
Chlorine  tablets  are  sold  for  home  use  or  for  camping  trips.  Some 
city  health  departments  furnish  them  free  or  sell  them  at  cost  to 
people  who  plan  to  spend  their  vacations  camping.  The  tablets 
may  be  used  according  to  directions  accompanying  them  to  rid 
water  of  all  dangerous  germ  life.  They  are  exceedingly  con- 
venient to  have,  especially  when  time  or  means  is  lacking  for  the 
boiling  of  suspected  water.  All  campers  should  be  supplied  with 
them. 

Water  from  ponds,  lakes,  or  running  stream  in  truly  wild  regions 
is  generally  safe.  If  water  is  uncontaminated  by  animal  refuse, 
it  will  not  cause  disease,  no  matter  how  much  decaying  vegetation 
there  may  be  in  it.  Sometimes  the  murky  water  of  ponds  or  even 
swamps  is  purer  than  the  clear  water  of  running  streams,  which 
may  be  polluted  by  careless  campers  upstream.  The  murky 
water  of  ponds  or  swamps  may  be  clarified  by  the  digging  of  an 
Indian  well. 

A  few  feet  from  the  edge  of  the  pond  or  swamp,  dig  a  hole  from 
12  to  18  niches  in  diameter,  with  the  bottom  of  the  hole  extending 
6  inches  below  the  water-level  of  the  swamp  or  pond.  Let  the 
water  seep  into  it  and  then  bail  it  out  quickly.  Repeat  this  process 
at  least  three  times.  After  the  third  or  fourth  bailing,  the  Indian 
well  will  be  filled  with  filtered  water. 

If  you  are  at  all  in  doubt  as  to  the  purity  of  the  water,  either 
boil  it  or  use  the  chlorine  tablets  as  directed. 

PROJECT  LIV.  —  How  to  Exterminate  the  Mosquito,  pages  452- 
454  (Community  Project) 

This  is  a  community  project,  except  in  rural  districts  where 
houses  are  widely  separated.  But  in  the  city  or  village  it  does  no 
good  whatever  to  destroy  the  breeding  places  of  mosquitoes  on  your 
own  premises  if  your  neighbors  provide  favorable  conditions  for 


PROJECTS  633 

them  either  on  their  own  premises  or  on  adjoining  vacant  lots. 
In  New  Orleans,  Havana,  the  Panama  Canal  Zone,  and  many  other 
places,  intelligent  and  concerted  effort  has  eliminated  the  mosquito 
as  an  agent  of  disease.  Any  community  may  accomplish  the  same 
thing. 

In  order  to  fight  the  mosquito  intelligently,  we  must  know  some- 
thing of  the  way  the  pest  comes  into  the  world.  When  one  realizes 
that  one  female  mosquito  lays  from  75  to  300  eggs  at  a  time  and  that 
these  eggs  develop  into  full-grown  mosquitoes  in  from  10  to  13  days, 
one  does  not  wonder  at  the  clouds  of  mosquitoes  that  sometimes 
infest  low  swampy  places. 

Mosquito  eggs  are  laid  at  night  or  in  the  early  morning  on  the 
surface  of  stagnant  water.  Mosquitoes  avoid  running  water  or 
fresh  water  that  is  frequently  stirred.  In  about  24  hours  in  warm 
weather  —  or  somewhat  longer  if  the  temperature  is  not  high  — 
the  eggs  hatch  into  the  larva  stage.  The  larva,  or  "wiggletail," 
which  almost  everyone  has  seen  in  stagnant  pools  or  rain  barrels, 
spends  most  of  its  time,  head  downward,  just  under  the  surface  of 
the  water.  It  keeps  the  tip  of  its  tail  (where  the  opening  of  its 
breathing  tube  is  located)  almost  constantly  at  the  surface  of  the 
water.  In  fact,  the  larva  cannot  live  more  than  a  minute  or  two  if 
it  is  unable  to  reach  the  surface  to  breathe.  After  seven  days  or  more, 
according  to  the  temperature,  the  developing  mosquito  passes  from 
the  larva  to  the  pupa  stage.  After  living  in  the  water  in  the  pupa 
stage  for  three  days  or  more,  it  finally  emerges  as  a  full-grown  mos- 
quito. 

Mosquitoes  do  not  fly  far  from  the  places  where  they  are  hatched ; 
hence,  if  they  can  be  kept  from  breeding  near  human  habitations, 
the  problem  of  mosquito  riddance  is  solved. 

Drainage.  —  Since  stagnant  water  furnishes  breeding  places  for 
mosquitoes,  the  first  work  to  be  done  is  to  drain  all  unnecessary 
ponds  or  pools.  Very  often  valuable  land  may  be  reclaimed  by 
the  very  process  of  draining  that  rids  a  section  of  mosquitoes. 

Kerosene.  —  Where  it  is  impracticable  to  drain  pools,  puddles,  or 
marshes,  the  surface  of  the  water  may  be  covered  with  kerosene. 
On  small  pools  or  tanks  it  is  necessary  only  to  pour  the  kerosene 


634  EVERYDAY  SCIENCE 

on  the  surface  of  the  water.  It  will  spread  in  an  even  film  over 
the  entire  surface.  On  marshes  or  large  ponds,  where  weeds  and 
intervening  dams  of  mud  prevent  the  film  of  oil  from  spreading 
over  the  entire  surface  of  the  water,  it  is  best  to  use  a  sprayer.  In 
either  case,  use  about  1  pint  for  approximately  every  20  square 
feet  of  water  surface. 

This  film  of  kerosene  kills  all  eggs  at  the  surface  of  the  water, 
suffocates  the  larva  or  "wigglers,"  by  cutting  off  their  air  supply, 
and  destroys  all  adult  female  mosquitoes  that  try  to  lay  their  eggs 
on  the  surface  of  the  water. 

It  takes  about  a  week  or  ten  days  for  the  oil  to  evaporate  from 
the  surface  of  the  water,  and  at  least  10  days  after  that  before  a 
hew  generation  of  mosquitoes  can  be  hatched.  It  is  a  safe  plan, 
therefore,  to  apply  kerosene  to  the  surface  of  all  stagnant  pools 
about  twice  a  month.  In  covered  tanks,  cesspools,  etc.,  one  appli- 
cation a  month  is  sufficient,  because  evaporation  does  not  take 
place  so  rapidly  from  such  unexposed  places.  In  heavy  soil,  cow 
tracks  and  other  small  depressions  may  hold  water  long  enough  to 
hatch  a  generation  of  mosquitoes.  After  every  rain,  such  de- 
pressions should  be  drained  or  else  sprayed  with  kerosene. 

Fish.  —  Where  pools  are  used  for  the  watering  of  stock,  kerosene 
cannot  be  used,  of  course.  In  such  cases,  the  remedy  lies  in  stock- 
ing the  ponds  with  top  minnows  or  sunfish.  These  fish  feed  on  the 
larva  of  the  mosquito.  If  there  are  no  other  fish  in  the  pond,  the 
top  minnow  may  be  used.  If  the  pond  is  stocked  with  larger  fish, 
the  sunfish,  sometimes  called  "pumpkin-seed,"  is  to  be  preferred 
because  it  is  able  to  protect  itself  by  means  of  its  rays  against  larger 
fish.  Do  not  neglect  to  drain  cow  tracks  around  such  ponds,  or 
else  spray  them  with  kerosene  often  enough  to  prevent  mosquitoes 
breeding  in  them. 

Screening.  —  Water  tanks,  rain  barrels,  cisterns,  and  other  re- 
ceptacles for  water  for  the  household  cannot  be  treated  with  kero- 
sene. Careful  screening  of  all  the  openings  of  these  receptacles 
is  the  only  remedy.  The  only  effective  screening  against  mosqui- 
toes is  the  16-mesh  screen —  16  wires  to  the  inch.  No  one  argues  for 
less  than  a  14-mesh  screen,  and  most  authorities  insist  on  a  16-mesh. 


PROJECTS  635 

If  your  house  is  equipped  with  screens  of  larger  mesh  and  you 
are  troubled  with  mosquitoes  that  squeeze  in  between  the  wires, 
rub  the  screens  every  night  before  dark  with  a  cloth  moistened  with 
kerosene.  If  you  dislike  the  odor  of  kerosene,  try  the  more  expen- 
sive oil  of  pennyroyal. 

Tin  Cans  as  Breeding  Places.  —  A  single  tin  can  may  catch  enough 
water  from  a  rain  to  breed  a  multitude  of  mosquitoes.  Before  tin 
cans  are  thrown  on  the  rubbish  heap,  punch  them  full  of  holes  or 
knock  the  bottoms  out  of  them.  Tin  cans  carelessly  thrown  on 
vacant  lots  make  a  neighborhood  look  slovenly  and  furnish  homes 
for  immense  families  of  neighborhood  mosquitoes. 

The  following  Farmers'  Bulletins  dealing  with  the  subject  of 
mosquitoes  may  be  had  on  application  to  the  United  States  De- 
partment of  Agriculture,  Washington,  D.  C. : 

"Some  Facts  about  Malaria,"  Farmers'  Bulletin  No.  450. 

"The  Yellow  Fever  Mosquito,"  Farmers'  Bulletin  No.  547. 

"Remedies  and  Preventives  against  Mosquitoes,"  Farmers'  Bul- 
letin No.  444. 


PROJECT  LV.  —  How  to  Fight  the  Fly,  pages  454-455  (Commu- 
nity Project) 

Fighting  the  fly  is  not  an  individual  project ;  it  is  a  community 
project.  If  you  live  in  a  small  town,  you  may  be  able  to  interest 
various  organizations  in  the  project.  If  you  live  in  a  large  city, 
you  may  be  able  to  wake  up  your  neighborhood.  You  can  do  some- 
thing and  should  do  everything  in  your  power  on  your  own  premises ; 
but  cooperation  is  necessary  if  the  fly  is  to  be  conquered. 

Boy  Scouts,  Neighborhood  Improvement  Clubs,  Civic  Leagues, 
Women's  Clubs,  High  School  Science  Clubs,  Commercial  Clubs, 
Chambers  of  Commerce,  and  other  organizations  have  succeeded 
in  making  some  communities  almost  flyless.  The  community  must 
be  educated  to  the  menace  of  the  fly  before  anything  worth  while 
can  be  accomplished,  and  this  requires  the  combined  effort  of  civic 
clubs.  Some  day  people  will  wonder  that  we  tolerated  such  a  men- 


636  EVERYDAY  SCIENCE 

ace  exactly  as  we  wonder  at  the  unsanitary  living  conditions  com- 
mon centuries  ago. 

The  average  life  of  a  fly  is  about  three  weeks.  Most  of  the 
millions  of  flies  that  do  not  die  of  natural  causes  during  the  summer 
succumb  to  fungous  diseases  in  the  fall  or  to  the  cold  of  early  winter. 
But  in  almost  every  house  a  few  survive.  They  hide  in  all  sorts  of 
warm  crevices,  where  they  pass  the  winter  in  a  state  of  complete 
rest.  The  number  of  flies  that  may  be  descended  in  one  summer 
from  one  wintered-over  fly  runs  into  the  trillions !  The  moral  is  : 
clean  and  disinfect  every  crevice  of  your  house  in  March  and  swat 
the  wintered-over  fly. 

Screen  all  porches,  windows,  and  doors  in  fly  time. 

Make  all  vaults  fly-proof  with  screening,  and  cover  the  contents 
once  a  week  with  copperas  or  iron  sulphate  to  disinfect  them  and 
to  prevent  the  development  of  fly  maggots. 

Keep  all  garbage  covered  tightly  until  it  is  disposed  of.  To  kill 
all  flies  in  and  around  garbage  pails,  sprinkle  formaldehyde  solution 
—  1  part  formalin  to  10  parts  water  —  in  and  around  the  pails  once 
a  week. 

Make  traps  and  set  them  near  doors  and  other  places  where  flies 
congregate.  Patterns  and  detailed  instructions  for  making  an 
effective  fly  trap  may  be  had  by  sending  five  cents  in  stamps  to 
the  Agricultural  Extension  Department  of  the  International  Har- 
vester Company,  Chicago.  See  also  Farmers'  Bulletins  Nos.  734 
and  927. 

All  flies  breed  in  filth.  Ninety  per  cent  of  all  flies  breed  in  stable 
filth !  This  should  be  hauled  away  and  spread  as  fertilizer  at  least 
once  a  week.  If  this  cannot  be  done,  keep  it  in  tightly  covered 
boxes  or  pits  until  it  is  removed.  Farmers'  Bulletin  No.  851  gives 
detailed  instructions  for  the  extermination  by  some  means  or  other 
of  flies  that  breed  in  stable  filth.  See  that  ordinances  are  passed  and 
enforced  against  all  people  who  maintain  live  stock  in  a  community. 

For  organizations  that  wish  to  conduct  a  fly  campaign,  the  fol- 
lowing books  and  pamphlets  will  prove  of  great  value  : 

"Farmers'  Bulletin"  No.  851.  This  treats  of  the  life  history  of 
the  fly,  of  its  carriage  of  disease,  its  natural  enemies,  control  measures, 


PROJECTS  637 

preventive  measures  for  communities  and  farms,  and  directions 
for  community  campaigns. 

"The  House  Fly,"  L.  O.  Howard.  Frederick  A.  Stokes  Co.,  New 
York. 

"The  Reduction  of  Domestic  Flies,"  Edward  H.  Ross.  J.  B.  Lip- 
pincott  Co.,  Philadelphia. 

PROJECT  LVI.  —  How  to  Make  War  on  the  Rat,  page  454 
(Community  Project) 

Among  all  mammals,  the  rat  is  the  worst  pest  known  to  man. 
Individual  war  against  rats  on  one's  own  premises  is  more  effective 
than  individual  war  against  flies,  but  only  united  effort  in 'com- 
munities can  achieve  permanent  results.  The  loss  of  approximately 
150  millions  of  dollars  a  year  from  the  depredations  of  rats,  aside 
from  the  menace  of  disease  they  offer,  is  too  great  a  tax  for  the 
United  States  to  tolerate  indefinitely. 

The  first  thing  to  do  on  one's  premises  is  to  see  that,  by  means 
of  steel,  concrete,  and  wire  netting,  all  construction  is  made  rat- 
proof.  This  applies  not  only  to  homes,  but  also  to  barns,  granaries, 
poultry-houses,  drains,  sewers,  etc.  The  saving  will  more  than  pay 
for  the  extra  cost  of  construction. 

Keep  all  garbage  cans  tightly  covered,  and  leave  no  scraps  of 
food  of  any  sort  exposed  on  your  premises  as  a  lure  to  rats  and  mice. 

Trapping  is  the  safest  method  of  dealing  with  rats  that  have 
gained  access  to  buildings,  such  as  homes,  stables,  warehouses, 
mills,  factories,  etc.  The  baited  spring  trap  may  occasionally 
catch  inexperienced  young  rats,  but  it  seldom  fools  the  wise  old 
ones.  Rats  are  very  wary,  and  they  seem  to  recognize  bait  by  its 
position  as  well  as  by  the  odor  of  human  hands.  Of  all  traps  for 
the  catching  of  rats,  none  is  so  satisfactory  as  the  smallest  "New- 
house"  game  trap.  Place  unusual  food  —  grain  if  the  rats  have 
been  feeding  on  meat ;  meat  if  they  have  been  feeding  on  grain  — 
where  they  can  have  easy  access  to  it,  and  allow  them  to  feed  freely 
on  it  for  several  days.  Then  set  the  spring  traps  in  these  places, 
with  the  trigger  very  lightly  caught. 


638  EVERYDAY  SCIENCE 

Do  not  put  anything  under  the  "pan"  of  the  trap;  and  do  not 
put  any  bait  inside  the  circle  of  the  open  jaws  of  the  trap.  Sprinkle 
food  about  the  traps  so  that  the  rats  will  be  likely  to  step  on  the 
pans  when  they  pick  it  up.  Cover  the  trap  with  chaff,  bran,  or 
earth  and  sprinkle  a  little  oil  of  aniseed  around  the  traps.  Be  sure 
that  the  trap  is  so  fastened  that  the  rat  may  drag  it  around  a  few 
feet.  Do  not  set  the  traps  in  the  same  place  twice  in  succession. 
These  traps  set  in  rat  runways  along  building  walls,  ditch  walls, 
or  at  the  mouths  of  rat  burrows,  or  on  their  trails  to  water  will  catch 
many  a  rat.  In  fact  persistent  use  of  traps  will  eventually  rid  a 
place  of  rats.  But  remember  that  it  frequently  requires  not  one 
but  many  traps,  and  more  patience  and  shrewdness  than  the  rats 
themselves  have.  Trapping  mice  is  merely  a  matter  of  baiting 
and  setting  the  traps,  but  trapping  rats  is  a  test  of  skill. 

French  cage  traps  can  never  be  used  with  success  without  a  period 
of  baiting.  Put  freshly  fried  bacon,  cheese,  grain,  or  any  other 
tempting  bait  into  the  trap  every  night  for  several  nights  and  leave 
the  back  door  of  the  trap  open.  When  the  rats  have  become  bold 
about  entering  and  eating,  bait  the  trap  as  usual  and  close  the  back 
door.  After  you  have  made  your  catch,  set  the  trap  in  another 
place  and  repeat  the  process. 

Poisons  are  not  safe  for  use  in  buildings  or  on  city  premises. 
Rats  are  too  inconsiderate  about  choosing  a  place  to  die.  Barium 
carbonate,  mixed  with  egg  and  made  into  a  paste  with  meal  or 
breadcrumbs,  is  a  cheap  and  effective  poison.  It  is  also  about  the 
safest  poison  because  in  small  quantities  it  is  not  dangerous  to 
domestic  animals. 

For  fighting  rats  on  farms,  Farmers'  Bulletin  No.  896  offers  a 
wide  range  of  sound  advice.  See  also  Bulletin  No.  33,  Biological 
Survey,  United  States  Department  of  Agriculture. 

PROJECT  LVII.  —  How  to  Read  an  Electric   Meter   and  Compute 
the  Cost  of  Current,  pages  486-487 

In  order  to  understand  a  few  terms  that  are  used  in  measuring 
electrical  energy,  let  us  liken  the  invisible  electric  current  to  a  stream 


PROJECTS  639 

of  water.  The  electric  stream  may  vary  in  size  as  does  a  stream 
of  water.  We  speak  of  a  stream  of  water  as  running  so  many  gallons 
per  second.  The  size  of  the  electric  current  we  measure  in  amperes. 
For  example,  only  a  small  stream  of  one-half  ampere  is  required 
to  run  an  ordinary  incandescent  lamp  of  16-candle  power,  but  a 
large  stream  of  five  amperes  is  necessary  to  run  an  electric  iron. 

It  is  in  connection  with  the  size  of  the  stream  of  electricity  in  a 
house  that  fuses  serve  the  purpose  of  safety  devices.  For  example, 
suppose  your  electric  company  has  a  15-ampere  fuse  on  your  din- 
ing room  circuit.  Now  suppose  you  are  operating  on  this  circuit 
two  16-candle  power  incandescent  lamps,  each  requiring  one-half 
ampere ;  and  a  toaster  and  a  chafing-dish,  each  requiring  5  amperes. 
This  makes  a  total  of  11  amperes.  If  now  you  add  a  percolator,  re- 
quiring 5  amperes,  all  the  devices  on  the  circuit  together  would  de- 
mand a  current  of  16  amperes,  and  the  overstrain  would  blow  the 
15-ampere  fuse  on  that  circuit. 

The  remedy  is  to  put  in  a  new  15-ampere  fuse,  and  not  to  use  so 
many  devices  on  the  circuit  at  the  same  time.  Or  it  may  be  that 
the  company  will  allow  you  a  20-ampere  fuse  on  that  circuit,  so 
that  you  may  use  all  the  devices  at  the  same  time.  But  do  not  use 
fuses  of  larger  amperage  without  the  consent  of  your  electric  company, 
because  your  wiring  may  not  safely  carry  a  larger  stream.  If  the  fuse 
should  be  of  larger  amperage  than  the  wiring  would  carry,  an  over- 
load would  burn  out  the  wiring  instead  of  the  fuse.  There  must 
always  be  a  safe  margin  between  the  size  of  stream  your  wiring  will 
carry  and  the  size  of  stream  your  fuses  will  withstand. 

Water  at  the  faucet  is  under  a  certain  number  of  pounds  of 
pressure  (p.  201).  This  pressure  has  nothing  to  do  with  the  size  of 
the  stream.  For  example,  you  may  open  the  faucet  only  slightly 
and  get  a  very  small  stream  of  water  or  you  may  open  it  wide 
and  get  a  full  stream.  The  pressure  behind  both  streams  is  the 
same.  What  corresponds  to  pressure  in  a  stream  of  electricity  is , 
measured  in  volts.  The  most  common  "pressure"  or  voltage  for 
a  lighting  circuit  is  110  to  120  volts. 

The  power  of  a  stream  of  water  flowing  from  a  faucet  depends 
on  the  size  of  the  stream  and  the  pressure  behind  it.  The  power 


640  EVERYDAY  SCIENCE 

of  an  electric  current  depends  on  the  size  of  the  current  (amperage), 
and  the  "pressure,"  or  voltage.  This  power  is  measured  in  watts. 
The  number  of  watts  may  be  determined  accurately  for  one  kind 
of  current  and  approximately  for  the  other  by  simply  multiplying 
the  number  of  amperes  by  the  number  of  volts.  For  example,  an 
electric  iron  using  a  current  of  5  amperes  under  pressure  of  110 
volts  requires  550  watts  of  electrical  energy  to  keep  it  heated.  If 
this  iron  is  used  for  an  hour,  we  say  that  it  consumes  550  watt- 
hours  of  current. 

But  a  watt-hour  indicates  so  small  an  amount  of  current  that 
the  commercial  unit  of  measurement  is  the  kilmvatt-hour,  1000 
watts  for  an  hour's  time.  Another  way  of  putting  it  is  that  1  kilo- 
watt-hour =  1000  watt-hours. 

Your  electric  fixtures  are  marked  with  the  number  of  amperes 
and  volts  necessary  to  run  them.  The  iron  mentioned  above  would 


KILOWATT  HOURS 

FIGURE  20.  —  DIAL  OP  A  WATT-HOUR  METER. 

be  marked  "5  amperes,  110  volts."  In  an  hour's  time  this  would 
consume  550  watt-hours  of  current,  as  has  been  shown.  This  is 
T.WTT,  or  .55,  kilowatt-hour.  If  your  company  charges  10  jf  a  kilo- 
watt-hour, it  costs  you  .55X$.10,  or  $.055,  to  operate  your  electric 
iron  for  an  hour. 

An  electric  stove  with  all  the  switches  open  requires  an  electric 
stream  of  about  20  amperes.  On  a  110- volt  current  such  a  stove 
in  full  operation  would  consume  in  an  hour  2200  watt-hours  of 
current.  This  is  ttjft,  or  2.2,  kilowatt-hours.  At  10  t  a  kilowatt- 
hour,  such  an  electric  stove,  with  all  the  "burners"  going,  would 
cost  2.2XS.10,  or  $.22  an  hour. 


PROJECTS  641 

An  incandescent  lamp  marked  40  watts  indicates  that  it  uses 
40  watts  of  current  per  hour.  A  40-watt  incandescent  lamp  would 
therefore  burn  25  hours  ( 1000  H- 40)  before  it  registered  1  kilowatt- 
hour,  or  10  t  worth  of  current. 

Reading  the  electric  meter,  or  watt-hour  meter  (as  it  is  called) 
is  exactly  the  same  as  reading  the  water  meter,  except  that  the  unit 
is  kilowatt-hours,  and  the  100,000  circle  is  missing.  Beginning  at 
the  right  and  reading  to  the  left,  the  circles  indicate  units,  tens, 
hundreds,  thousands.  The  dial  in  Figure  20  reads  538  kilowatt- 
hours. 

Notice  that  the  hand  in  the  tens  circle  is  in  a  doubtful  position. 
It  must  be  read  30  because  the  hand  in  the  unit  circle  has  not  yet 
reached  0.  (See  Caution,  Project  XXXII.) 

PROJECT  LVIII.  —  How  to  Attach  Wires  to  a  Socket,  page  488 

Caution.  If  you  wish  to  attach  a  socket  to  the  wiring  of  your  house, 
be  sure  to  open  the  switch  at  the  fuse  board,  thus  turning  off  the  cur- 
rent from  your  house  wires. 

First  remove  the  shell  from  the  cap  of  the  socket  (A,  Figure  21). 
If  the  shell  is  attached  by  screws  or  rivets,  turn  it  to  the  left  and 
pull  it  off.  If  the  socket  is  old,  the  screws  in  the  cap  may  have 
to  be  loosened.  If  the  shell  has  a  corrugated  upper  edge  that  springs 
into  the  cap,  it  may  be  removed  by  pressing  it  firmly  near  the  key 
(the  place  is  indicated  on  most  shells  by  the  word  "Press")  and 
pulling  it  out  of  the  cap. 

Notice  that  the  cap  and  shell  are  completely  lined  with  insulating 
material.  If  the  insulating  material  is  missing  or  damaged,  do 
not  use  the  socket ;  it  is  dangerous. 

Cut  off  the  ends  of  the  two  wires  even.  P^emove  the  insulation 
from  the  ends  of  the  wires  just  far  enough  back  to  allow  bare  wire 
ends  to  fit  under  the  attachment  screws  of  the  core  (A,  Figure  21). 
To  do  this,  cut  through  the  braided  cover  and  scrape  off  the  in- 
sulation around  the  wires.  In  removing  this  insulation,  be  very 
careful  not  to  cut  the  filaments  of  wire  within. 

When  the  insulation  is  removed,  roll  the  exposed  filaments  of 


642 


EVERYDAY  SCIENCE 


/— ^ 


wire  between  your  thumb  and  forefinger  into  a  compact  strand 
that  will  fit  snugly  under  the  screws  of  the  core. 

Slip  the  cap  over  the  two  wires,  as  in  A,  Figure  21.     Loosen  the 
attachment  screws  on  the  core,  bend  a  wire  end  around  each  of  the 
-TT^  two  screws  in  clockwise  direction,  and 

f^~~  tighten  the  screws  again. 

Replace  the  shell.  If  it  is  attached 
to  the  cap  by  screws,  slip  the  screws 
into  the  grooves  and  turn  the  shell  to 
the  right.  If  it  is  the  spring  type  of 
shell,  -push  the  upper  edge  of  it  into 
the  cap  until  you  hear  it  click. 

If  you  succeed  in  taking  a  socket 
apart  and  wiring  it,  you  will  have  no 
difficulty  in  taking  almost  any  sort  of 
plug  apart  and  attaching  wires  to  it. 
Just  be  careful  to  put  the  parts  back 
in  the  order  in  which  you  removed 
them.  Figure  21,  B,  shows  one  type  of 
attachment  plug. 

Two  of  the  most  interesting  and  practical  books  on  electricity 
for  beginners  are : 

"The  American  Boys'  Book  of  Electricity,"  Charles  H.  Seaver. 
David  McKay. 

"  Harpers'  Electricity  Book  for  Boys,"  Joseph  H.  Adams.  Harper 
&  Bros. 


PROJECT  LIX.  —  How  to  Make  the  Acquaintance  of  Trees  and  Wild 
Flowers  (Independent  Project) 

Projects  LIX  and  LX  are  independent  projects,  not  specifically 
connected  with  any  particular  portion  of  the  text  of  this  book. 
But  in  a  larger  sense,  they  are  very  vitally  related  to  the 
entire  book.  One  of  the  chief  purposes  of  Everyday  Science  is 
to  encourage  an  interest  in  the  great  out-of-doors.  No  one  can 


PROJECTS  643 

spend  much  time  out  of  doors  without  having  a  desire  to  become 
better  acquainted  with  the  birds,  trees,  and  undergrowth.  Unfor- 
tunately, wild  forest  life  is  so  scarce  in  most  thickly  settled  regions, 
that  few  boys  and  girls  have  the  opportunity  to  make  a  study 
of  it. 

Guidance  for  the  study  of  outdoor  life  cannot  be  given  except 
in  books  devoted  wholly  to  that  purpose.  As  a  general  guide  for 
beginners  in  the  study  of  the  out-of-doors,  probably  no  book  excels 
the  "Official  Handbook  of  the  Boy  Scouts  of  America  "  (200  Fifth 
Avenue,  New  York).  "The  Book  of  Woodcraft,"  by  Ernest 
Thompson  Seton  (Doubleday,  Page  &  Co.)  is  another  book  in 
which  boys  and  girls  devoted  to  outdoor  life  can  find  a  mine  of 
interesting  and  valuable  information. 

Among  the  best  guides  to  the  study  of  trees  and  wild  flowers  are 
the  following  books : 

"Field  Book  of  American  Trees  and  Shrubs,"  F.  Schuyler 
Mathews.  G.  P.  Putnam's  Sons.  No  other  one  book  is  as  satis- 
factory as  this  for  the  identification  of  trees  and  shrubs. 

"Studies  of  Trees,"  J.  J.  Levison.  John  Wiley  and  Sons. 
This  is  probably  the  most  satisfactory  all-around  book  for  be- 
ginners on  the  identification  of  common  trees,  choice  of  shade  trees, 
care  of  trees,  and  elementary  forestry. 

"The  Tree  Guide,"  Julia  Ellen  Rogers.  Doubleday,  Page  &  Co. 
A  convenient  pocket-size  guide  that  enables  the  forest  rambler 
to  identify  trees  by  their  foliage. 

"The  Forester's  Manual,"  Ernest  Thompson  Seton.  Double- 
day,  Page  &  Co.  A  guide  to  the  trees  of  Eastern  North  America, 
with  maps  showing  the  distribution  of  each  tree  described. 

"The  Trees  of  California,"  Willis  Linn  Jepson.  Cunningham, 
Curtiss  and  Welch,  San  Francisco. 

"Field  Book  of  American  Wild  Flowers,"  F.  Schuyler  Mathews. 
G.  P.  Putnam's  Sons.  This  is  the  most  satisfactory  handbook  for 
the  identification  of  wild  flowers.  Its  abundance  of  illustrations 
makes  it  particularly  useful  to  the  beginner  or  amateur. 

"Wild  Flowers  Every  Child  Should  Know,"  Frederic  William 
Stack.  Doubleday,  Page  &  Co.  A  valuable  feature  of  tin's  book 


644  EVERYDAY   SCIENCE 

for  the  beginner  is  its  arrangement  of  the  most  common  wild  flowers 
according  to  color. 

"Wild  Flowers  of  the  North  American  Mountains,"  Julia  W. 
Henshaw.  Robert  M.  McBride  Co.  This  is  a  beautiful  guide  to 
the  flowers  of  the  Rockies. 

"Field  Book  of  Western  Wild  Flowers,"  Margaret  Armstrong. 
G.  P.  Putnam's  Sons.  A  very  satisfactory  guide  to  the  wild  flowers 
of  the  regions  west  of  the  Rockies. 

"Flower  Guide,"  Chester  A.  Reed.  Doubleday,  Page  &  Co.  A 
pocket-size  guide  illustrated  in  color  for  the  forest  rambler. 

PROJECT  LX.  —  How  to  Study  Bird  Life  (Independent  Project) 

Three  bulletins  of  the  United  States  Department  of  Agriculture 
make  a  very  good  introduction  to  the  study  of  the  common  birds : 

"Fifty  Common  Birds,"  Farmers'  Bulletin  No.  513  (15  0). 

"Bird  Houses  and  How  to  Build  Them,"  Farmers'  Bulletin  No. 
609. 

"The  English  Sparrow  as  a  Pest,"  Farmers'  Bulletin  No.  493. 

Among  the  most  reliable  and  usable  manuals  for  the  identification 
of  North  American  birds  are  the  following : 

"What  Bird  Is  That?"  Frank  M.  Chapman.  D.  Appleton  & 
Co.,  1920.  This  is  the  most  usable  handbook  of  birds  for  the  United 
States  east  of  the  Rocky  Mountains.  Every  land  bird  in  that  section 
is  pictured  in  color.  The  color  plates  group  the  birds  according  to 
season,  and  indicate  the  relative  sizes  of  birds.  The  accompanying 
text  is  simple  but  thoroughly  adequate.  This  is  not  an  expensive 
book. 

"Color  Key  to  North  American  Birds,"  Frank  M.  Chapman. 
D.  Appleton  &  Co.,  1912.  The  title  indicates  the  character  of  this 
book.  It  is  a  guide  to  bird  study  throughout  the  North  American 
continent. 

"  Birds  of  the  Rockies,"  Leander  S.  Keyser.    A.  C.  McClurg  &  Co. 

"  Birds  of  California,"  Irene  Grosvenor  Wheelock.  A.  C.  McClurg 
&Co. 


PROJECTS  645 

"Handbook  of  Birds  of  the  Western  United  States,"  Florence 
M.  Bailey.  Houghton  Mifflin  Co.,  1917.  This  is  a  complete  guide 
for  the  great  plains,  the  great  basin,  the  Pacific  slope,  and  the 
lower  Rio  Grande  valley. 

Among  the  most  interesting  books  about  birds  are  the  following : 

"  Bird  Friends,"  Gilbert  H.  Trafton.    Houghton  Mifflin  Co.,  1916. 

This  treats  of  the  life  of  birds,  their  economic  value,  the  enemies 
of  birds,  the  protection  of  birds,  and  methods  of  attracting  them. 

"Wild  Bird  Guests;  How  to  Entertain  Them,"  E.  H.  Baynes. 
E.  P.  Dutton  &  Co.,  1915. 

"Homing  with  the  Birds,"  Gene  Stratton-Porter.  Doubleday, 
Page  &  Co.,  1919. 

"Methods  of  Attracting  Birds,"  Gilbert  H.  Trafton.  Houghton 
Mifflin  Co.,  1910. 


INDEX 


References  are  to  pages 


Abdo'men      .     .     . 

Acids 

neutralization  of  . 
Adenoids 


...     410 
.  54-59,315 
.  55-59,31 
...     408 
Adiaba'tic  cooling  and  heating 

124-125,  221 

Agricultural  soils ;  see  Soils 
Air    ....     96-134, 135, 141, 152 
209-226,  279-283,  311,  313-314 
425, 443, 445,  483 
adia"batic  cooling  and  heating 

of 124-125,  221 

atmosphere  (earth's  envelope 

of  air)    .      .     .     96-97,114,115, 

120,  132-134, 141, 152, 209-213, 

279-280,  313-314 

bacteria  in  .  98-99, 120-122,  443 
composition  of  .  97-100, 132-133 
compression  of  123-125, 133-134 
condensation  of  .  .  104, 125-126 

density  of 116,132 

evaporation  of  moisture  in 

100-107,  133 

expansion  of  ...     109, 123-125, 
133-134 

humidity  of  (absolute ;    rela- 
tive ;  saturated)   .    102-107, 133 

hygrometer 103 

liquid  air 125 

precipitation  of  moisture  in 

101-104 

pressure  of      .     .     .   110,114-125, 
127-134,210-211 
saturation  of  moisture  in 

102-103, 104,  106, 112,  141 

temperature 100-107, 

109-110,  112,  125-128,  134 

vacuum  of 117-118 

ventilation     .     .    99,112-114,133 


Air  —  Continued 

water  vapor  in    ....   98-108, 
112, 127,  133, 141 

weight  of  ....      99,  108-110, 

114-115,129-131,133 

winds      110, 125,  215-226,  281-283 

Air  sacks 408 

Air  tubes 408 

Alcohol      .     .    105,140,431-432,457 

abuses  of 431-432 

evaporation  of 105 

solvent,  as 140 

Alimentary  canal     ....  419-421 

Alkali  soils 332 

Alkalies 55 

Altitudes 132, 134 

Ammonia  (a  gas) 127 

Angles  of  incidence  and  reflec- 
tion   352 

Angleworm ;  see  Earthworm 

Animals 98-100,  166, 

311-319,  345, 366, 399-421,  423, 
425-458, 522-553 
classification : 
by  distribution : 

amphibia 532 

land  animals     .     .       536-541 

sea  animals  .     .    166,  532-536 

phosphorescence     .  533-534 

by  structure : 

invertebrates     .    400-405, 423 

insects 400-405 

protozoa     400-401,423,452 
breeders    and    car- 
riers of  disease  401, 452 
see  also  Bacteria 

shellfish 400 

worms ....      317-319, 
345, 401-402 


EVERYDAY  SCIENCE 


References  are  to  pages 


Animals  —  Continued 

vertebrates  400,405-121,423, 
533-534 

amphibia,   birds,  fish, 
mammals,      marsu- 
pials, reptiles       .     .     400 
man  (a  mammal) ;  see 

Man 
dependents  (parasites  and 

saprophytes)     ....     397 

food  as  energy-maker  of   .     .    399, 

423, 425-458 

physical  features  of  earth  as 
affecting      ....       541-553 

Anther  (of  flower) 387 

Anti-cyclones 224 

Antit5xins 444 

Arcturus,  distance  from  ...         7 

Arid  lands 336-338 

Arteries  .  .  .  408-109,411-412 
Artesian  wells  ....  197-198 
Ash  (in  volcanic  eruptions)  .  .  504 
Asteroids  (planetoids)  ...  11 

Vesta 11 

Atmosphere ;  see  Air 

At'olls 549 

Atoms  ....    50-51,58,500,501 

electrons 500,501 

Attraction;     see    Earth,    Elec- 
tricity; Magnetism;  Matter 

Auditory  nerve •  .     418 

Auricles  (of  heart) 412 

Aurora  Bo-re-al'is  ("  Northern 

Lights") 360 

Axis  (of  earth)    .     .       8-9,25-31,39 
Axle,  wheel  and ;  see  Wheel  and 
axle 

Bacteria  .  .     .     .98-99, 120-122,  303, 

313-318,  361-362,  398-399, 

401,  422, 435-449,  516-517 

air,  general  purity  of    120-122, 443 

beneficent  435-438 

classes  and  varieties  of  .'398-399 
coal  and  peat  developed  by 

516-517 

decay  caused  by  ...  303,  315 
disease-breeding.  .  401,441-444 
fertilizers  of  soil,  as  315,  317-318 


Bacteria  —  Continued 

forms  of 438^39 

harmful       .    314,435-439,445-449 
food  spoiled  by     .     .     .445-449 
health    and    sanitation    vs. 

120-122,  444-447 

microbes 98,443 

nitrogen    prepared    for    life- 
uses  by   ...     98-99, 317-318 

number  of 314 

propagation  of  .  .  398-399, 422 
ptomaines  caused  by  .  .  .  439 
soils  developed  by  .  314,315-318 

structure  of 398 

water  polluted  by    .     .     .445-449 
see     also     Fungi ;       Molds ; 
Protozoa;  Yeasts 

Barograph 130 

Barometer  .  .  128-131,  134, 217 
Bars,  sand  ....  162,  258,  282 
Basalt  (ig'neous  rock)  ...  253 

Bases 54-59 

alkalies 55 

neutralization  of       .     .     55, 58-59 

Beach 161,251 

Bees  (honey-bees)        .     .     .  403-405 
Bell,   A.   G.   (inventor  of  tele- 
phone)    495 

Beverages  ....  431-432,456 
Birds  (vertebrate  animals)  .  .  400 
Blizzard  (snow  and  wind  storm)  228 

Blood 410-411 

corpuscles,  red  and  white-      .     411 

haemoglobin 411 

plasma 411 

Boiling  point .  100,  125-127, 134, 136 
Boracic  acid  (a  disinfectant)  .  445 
Borax  (an  aid  in  emulsifying)  .  146 

Brain 413,418 

Bread 437-438 

Breathing  (respiration)     .     .  407-410 
means    of    obtaining   energy 

from  air 407 

organs  utilized  in     ...  407—408 
Bridges,  natural  (of  Utah  and 

Virginia) 198 

Bubo'nic     plague      (protozoan 

disease) 454 

Bud  (of  plant) 377-378 


INDEX 


References  are  to  pages 


Budding   (plant-propagation)    .     377 

Buds  (of  yeasts) 399 

Buoyancy  of  water       ....     148 
Buttes  (of  plateaus)     .     .     .  272, 276 

Calms  (of  the  tropics)      ...     221 
Calorie  (measure  of  energy  and 

heat) 84 

specific  heat    ......      84 

Ca'lyx  (of  flower) 387 

Cambium  layer  (of  stem)      .  374,  377 

Canals 192-196,  336 

Candle  power  (standard  meas- 
ure of  light  intensity)   ...     350 
Canons  (of  plateaus)   ....     268 

Capes 258 

Capillaries  (of  circulatory  sys- 
tem)  409,411 

Capillary  action  (of  water)    .  170,  327 
Carbohydrates  383, 423,  425-428,  456 

composition  of 425 

food  properties  of     ...  425-428 
found  in  cereals  and  grains ; 

fruits;  vegetables  .     .     427 
amount  necessary  daily 

indict 428 

functions  of 425-428 

manufactured  in  green-plant 

leaves  .     .     .    383,423,425 

chlorophyll 382,383 

Carbolic  acid  (a  disinfectant)  444-445 

Carbon      .     .     .     399-400,425,456, 

488,  517-519 

constituent  of  food  ....     456 
for   incandescent    lamp    fila- 
ments       488 

in  coal  and  peat  ....  517-519 
Carbon  dioxide  .  98-99, 133, 144,  280 
constituent  of  air     98-99,  133,  280 
exhaled  by  animals  ....       98 
inhaled  by  plants     ....       99 
solvent  of  limestone      .     .     .     144 
weathering  agent  of  atmos- 
phere        280 

weight 99 

source  of  danger  in  mines  .       99 

Caverns 198 

Caves 198 

Mam.-noth  Cave       ....     198 


Cells  (of  plants)      .     .     .     .  371, 388 

structure  of 371 

protoplasm  in 371 

Centri'fugal  force    ....      43-47 
Centri'petal  force  ;  see  Gravita- 
tion ;  Gravity 

Chemical  action  .  .  .  .  72,  484 
Chemical  changes  ....  53,  58 
Chemical  compounds  .  .  .  54-59 
Chemical  energy  .  .  .  72-94, 358 
Chloride  of  lime  (a  disinfectant)  445 
Chlo'rophyll  382,  399,  400,  419,  425 

Choke  damp 99 

Cinders  (volcanic)  ....  504-506 

Circulation  (of  blood)     410-413,  423 

Circumference  (of  earth)      .  2,  23,  39 

Cities    ....     198-208,257-263, 

444-456, 457,  546-548 

locations  of     .       257-263, 546-548 

industries  due  to  ...  546-547 

sanitation  of   ...    444-456, 457 

water-supply  systems  of    .  198-208 

Clay  (of  ocean) 156 

Clayey    soils    .    307,   310,   319-320, 
345 

Cleanliness 451-455 

preventer  of  disease      .     .  451-455 
care  of  wounds     ....     451 
protector  of  health  .     .     .  452-455 
destruction     and     preven- 
tion of  harmful  bacteria 
and  protozoa-    .     .     .  452-455 

Cliffs 160 

Climate     .     .     .      238-244,245-246 

causes  of 238 

effects  of  day  and  night  upon     243 
effects   of    physical    features 

upon    .     .      238-243,245-246 
of  mountains   .     .    238-240,245 
of  water-bodies     .     .     .241-243 
effects    of    seasonal    changes 

upon 243-244,  245 

see  also  Weather 

Clouds.     .     .     .      102,104,133-134, 
210,  215,  244,  483 
condensation  of  atmospheric 

moisture 104 

electricity  in 483 

weather  vs 210,244 


EVERYDAY  SCIENCE 


References  are  to  pages 


Coal      ....      254-255,516-519 

anthracite 255 

bituminous 254 

mining  of 516-519 

story  of 516 

Coast,  depressed 549 

Coastal  plains     .      257-264,  274,  546 

see  also  Plains 

Cold-storage  .     .       125,  127-128, 134 
Color     ....      356-361,  364,  390. 

in  light 356 

refraction  through  prism  356-358 
spectrum      ....  357-358 
effects  of  atmospheric 

conditions .     .     .  357-361 
spectroscope .     .     .  358, 364 

of  flowers 390 

Combustion 71,97-98 

Comets 18, 19 

Halley's  Comet 17 

see  also  Sky 
Commercial  fertilizers      ...     316 

see  also  Fertilizers 
Compass,  mariner's  39,  476-478,  501 

dip  of  needle 477-478 

corrections  for  declination  .     478 

Conservation      .     .  37,  40,  63,  74-80, 

90-94,    108,    112-114,133,   184, 

198-206,  209-210,  307-346, 

362,  430-433,  438-441,  444- 

457, 462,  473 

of  energy    .     .     .     63-64,462,473 

of  food 440-441 

legitimate  preservation       .     440 
illegitimate    preservation  .     441 

of  forests 339-345 

of  fuels 74-77,  94 

of  health     ....    99,108,112- 

114, 133,  361-362,  430-433,  438- 

439, 443-457 

by  cleanliness  and  sanita- 
tion        444-457 

disinfection    361-362, 443-445 

sewage 449,457 

by  proper  food      .     .     .  455-457 

by  ventilation  .  99, 112-114, 133 

of  heat  .     .    77-80,  90-94,  209-210 

fire-control 77-80 

smoke  abatement      ...       94 


Conservation  —  Continued 

of  light 37,  40,  362 

daylight  saving  and  light- 
less  nights     .     .     .   37,40,362 
of  soils  .     .     .     184, 315, 322-323, 
329-332,  334, 339-345 
by  adding  and  conserving    • 

soil-water     ....  322-323 

by  cultivation  ....  329,  334 

by  draining       .     .     .     .  331, 334 

by  dry  farming     .     .     .  329-330 

alternate-year  planting  .     330 

by  fertilizing 334 

by  forestry 339-345 

by  irrigation    ....  330-332 

ditching 331 

flooding 330-331 

by  levees 184 

by  neutralizing  over-acida- 

tion 315 

by  prevention  of  seepage  .     331 
by    prevention    of    water- 
logging      331 

by  reclamation;     see  Rec- 
lamation 
see  also  Soils 
of  water-supply  ....  198-206 

Constellations 9-10, 19 

see  also  Stars 
Continental  shelf    .     .     .     .256-259 

bars 258 

dunes 258 

islands   ........     256 

lagoons 259 

life  on 257 

reefs 258 

see  also  Land 

Continents     ....    248, 256-276 
Contraction   (of  gases,   liquids, 

solids) 65-69,94 

Convection  currents     .     .     88-90, 94 

Coral  islands 510,  533 

polyps 533 

Corol'la  (of  flower)       ....     387 

Coro'nas 17,360,365 

Corpuscles  (of  blood)  .    411,430,444 

Crane 491 

Craters  (of  volcanoes) .    503-506,  549 
Crevasse'  (of  glaciers)      .     .     .     289 


INDEX 


References  are  to  pages 


Cribs  untakes) 204 

Crustaceans  (shellfish)  .     ..    533 

Cultivation ;  see  Soils 

Currents  .  .  110-111,161-162,484 

of  air 110 

of  electricity 484 

of  water 161-162 

Cylinder  (of  engine)     ....     471 

Darwin  (on  earthworm)   .     .     .     319 

Day  and  night    .     .     3, 12,  24-26,  33 

variations  in  length  of  .     .      24-26 

Daylight  saving  ....   37,  40,  362 

Decay 303,  315 

necessary  in  soil-making   .     .     315 

process  of 303 

see    also    Bacteria;      Molds; 

Protozoa ;  Yeasts 

Declination  (of  earth)       ...     478 
Degrees  (of  latitude  and  longi- 
tude)  32 

prime  meridian  (Greenwich)         32 

Deltas 189-190,549 

Density      .     66,  94,  116,  132, 137,  150 

of  air 116, 132 

of  water 137 

Deposition  and  erosion   252,  278-282 

Dew 104 

Dew-point      ....    102-104, 112 
Diameter  (of  earth)     ...  2,  23,  39 

Diaphragm 409 

Diastase .     383 

Diatoms 532 

Dic5tyle'dons 375-377 

Digestion  (of  food)       .     .     .  419-421 
alimentary  canal      .     .     .  419-421 

esSph'agus 420 

intestines 420-421 

mouth 420 

stomach 420 

Diphtheria  (bacterial  disease)    .     442 

Direction  (four  cardinal  points)  20,  24 

Disease     .       361-362,401,441-449, 

452-455, 457 

antitoxins 444 

bubonic  plague 454 

causes  of 454 

bacteria.     .      401,441-449,457 
prStozo'a     .      400,  452-455,  457 


Disease  —  Continued 

disinfection     .      361-362, 443-445 

malaria 452 

prevention  of .      361-362, 442-447 
"  sleeping  sickness  "  of  Africa  452 

source  of 443-447 

Texas  fever    • 454 

toxins 444 

typhoid  fever 442 

wound-infection 442 

yellow  fever    .     .     .     .     .     .     452 

see  also  Health  and  Sanitation 
Disinfection  .     .       361-362,443-445 

air 445 

chloride  of  lime 445 

drying 444 

soap 445 

solutions 444-445 

sunlight 444-445 

temperatures,  extremes  of      .     444 

water 445 

see  also  Health  and  Sanitation 
Ditching  (in  irrigation)     ...     331 

Divides,  land 175-176 

Doldrums 221 

Drainage ;  see  Soils 

Drowned  river  valleys      .     .  188-189 

Dry  farming 329 

Dunes,  sand 258,  283 

Dust  (volcanic) 283-285 

Dynamo 497 

Ear  (organ  of  hearing)     416-418, 423 

auditory  nerve 418 

bones  of 418 

drum  of 418 

Earth  (a  planet)      ....      20-41 
air  and  atmosphere ;  see  Air 
axis  and  poles  of       .  8,  9,  25-31,  39 
centrifugal    and    centripetal 

forces      .     .      43-49,58,93,326 
circumference  of .     .     .     .2, 23, 39 

climate 238-246 

clouds  and  precipitation    .     .    102, 
104,  133-134,  210,  215,  244,  483 
coasts ;  see,  below,  shores 

composition  of 42 

continents  and  islands .     .     .    248, 
256-276,540-541 


EVERYDAY   SCIENCE 


References  are  to  pages 


Earth  —  Continued 

crust  of,  see  below,  surface 

cycles  of  change 303 

day  and  night  .  3, 12,  24-26,  33 
development  of  earth-science  20 

diameter  of 2,  23,  39 

direction,  cardinal  points  of  20,  24 
distances  to  celestial  bodies 

from 2, 11,  23 

elements 51 

equator 30-31,39 

gravity.  .  .  .47-49,58,93,326 
harbors.  .  188-189,548-552,553 
interior  of ;  see,  below,  surface 
lakes  .  .  171-174,177-178,185 
magnetism  .  37-39, 475-480,  501 
meridians  and  parallels  .  .37 
minerals  and  mining  .  254-255, 
515-520,  542-543 

moon     ....      2,4,14-17,19, 
165,  210,  347-351 

mountains  and  hills      22,  238-241, 

248,  264-267,  541-543 

ocean     .     .     .     152-167, 249-251, 

256-258,  514,  531-535,  552 

physical  conditions  of  .     .  522-553 

plains     .     .     .     257-259,268-276, 

301-302,  544-548,  553 

planetary  movements  .     .      48-49 

revolution  of  ...    26-31,  39-40 

rivers     .     .     .       176-208,546-548 

rocks      .     .    252-255,275,279-281 

rotation  of       ....     23-26, 39 

seasons 27-31,40 

shape  of 21-23,  278 

shores      .     .     .    243-244,256-259, 
540-541,549, 

size  of 1-2,22-23 

soils  ....         57,173,197-198, 

209,  212-213,  284-286,  293-300, 

307-346, 401-403,  535 

storms 221-231 

surface  (crust)    outside   and 
within     .     166, 247-306, 502-553 

tides 17-19, 164-166 

volume 2 

waves  .  .  .  157-161,251,514 
weather  .  .  209-237,244-245 
winds  .  .  .  216-231, 244-245 


Earthquakes 513-515 

cause  of 513-514 

effects  of 514-515 

conflagrations   (San  Fran- 
cisco)   515 

ocean-waves  (Lisbon)    .     .     514 

Earth-science     ....   8-9,20-21 

Earthworms    .311-319,345,401-402 

fertilizers  of  soils      .    317-319,  402 

structure  of     ...    345, 401-402 

Ebb  tide 164,  166 

Eclipse 16, 17,  353 

of  earth's  moon 17 

of  Jupiter's  moons  ....  353 
of  sun  ..../....  353 

Eddies 165 

Egg  cell  (of  plants)      ....     388 

Eggs 427,430 

see  also  Food 

Electricity       .     .     .      62,72,94,350, 
472, 480-501 

atoms 500 

attraction  of   ......     483 

conductors  and  non-conduc- 
tors      482 

current' 484-487,500 

dry  cell 485 

electrodes 485 

electroplating  .  .  .  488-489 
electrotyping  ....  489-490 
energy  of  .  .  72-94,472,484,501 
Faraday's  discovery  .  .  .  497 

frictional 480 

heat  of 62, 486-487 

intensity  of 350 

law  of 350 

light  of 487-488,  501 

theory  of 500 

voltaic  cell 484-485 

see  also  Magnetism 

Electrodes 485 

Electrons 500-501 

Elements  (of  matter)  .     .     51-52,  58 

Elevation 259 

Em'bryo  (of  animal  and  plant 

life) 388-389,394 

Emulsion 144-146 

soap  an  emulsifier    ....     145 
borax  and  soda  as  aids  .     .     146 


INDEX 


References  are  to  pages 


Energy       .     .     .    57,60-94,98,100- 
107,  137-138,  350,  357-358,  396, 
399-400,  407-410,  419, 428-430, 
456, 459-474, 483-484,  501 
breathing  as  means  of  gen- 
erating      407-410 

by  combustion     .      72-94,  98,  399, 

419,  428-429, 472, 474 

by  evaporation    .....     101 

by  molecular  motion    .     .      67, 94 

law  of 67,94 

by  transference    ....  357, 474 

by  transformation    .   62-64,  72-94, 

357, 470-474 

conservation  of         63-64,  462,  473 

control  of  57 

evaporation  as  form  of      .  100—107 

food  as  generator  of     ...    399, 

419, 428,  430,  456 

forms  of 60-93,  396 

friction  vs.       ...      63, 462-463 
"  lost  energy  "      .      63,  462-463 

intensity  of 350 

kinds  of : 

chemical      .     .      62,72-94,358, 
472-473,  501 

electric  and  magnetic    .     72-94, 

472, 483-484,  501 

gravitational    .        62-63,93,483 

heat    .     61,93,137,357-358,501 

light  .     .     .     .     61,93,  357,501 

mechanical.     .     .     .    61,72-94, 

137-138,  470-474 

laws  of 67,  94,  350 

of  animals.     .     .  98,399,419,428 

of  plants 399 

power  generated  by      .     .     72-94, 

137-138, 470-474,  484,  501 

sun,  source  of      3,  03,  101,  396,  399 

Epiglottis 408 

Equator 30-31,39 

Equatorial  winds 220 

Erosion 159-101,186, 

252, 278-285 

by  ice 285 

by  water 278 

by  waves    159-161 

by  wind 281-282 

sand  an  agent 282 


Es'tuaries 261 

Ether 105,  361 

Evaporation  .     .      100-107, 127-128, 

133, 136, 153,  166,  170, 172, 186, 

278,  327-329,  331,  345,  385 

a  cause  of  salt  lakes      .     .     .     172 

cooling  by .     104 

in  irrigation 331 

of  alcohol 105 

of  ammonia  gas  ....  127-128 

of  ether 105 

of  gasoline       .     .     .    105, 140, 520 

of  water      .     .      100-107,  136,  153, 

166,  170,  278,  327-329,  345,  385 

moisture  in  plant-leaves     .     385 

rain-water 170 

sea-water 153, 166 

soil-water    .     .     .    327-329,345. 

process  of 100 

temperature  vs 100-106 

Expansion  64-69, 94, 124-125, 136-137 
Experiments  (The  experiment- 
number  is  in  bold  face) : 

air 35-43,97-111 

atmospheric  pressure    .     .    44-55, 

114-131 

earth's  magnetism    .     .     .     .  8, 37 

rotation 4-7, 24-33 

shape 2-3,22 

surface  80-87,248-279, 161 ,  5 1 2 
electricity  .  .  152-160,480-493 
energy  .  .  .  145-146,462-466 
food  .  .  .  138-144,419-438 

heat 18-34,  64-88 

life  animal       .      133-137, 402-417 

plant       .     .      108-123,367-385 

seed    .     .     .      124-132,393-396 

light  ....       100-107,  347-358 

magnetism       .       147-151, 475-478 

matter 9-15,42-55 

changes  of  .  .  .  16-17,51-55 
sky  (the  heavens)  .  .  .  .  1, 8 

soils 88  99,  :;n:  827 

water     ....     56  74,  135   170 

weather,  rainfall       .     .     .    79,231 

winds      .     .     .     75-78,216-218 

Extension 42,43 

Eye  (organ  of  sight)    .    414-416,423 
eyelid 114 


EVERYDAY  SCIENCE 


References  are  to  pages 


Fall  line  (of  rivers)       .     .     .  547-548 

Faraday's    discovery  .     .     .  495-497 

Farm  and  garden    ....  307-346 

base  of  civilized  life      ...     307 

building       material       anu 

clothing 307 

Fats  and  oils       .      423, 425-429, 456 

carbohydrates 425 

food  properties  of     ...  425-428 

functions  of 425-429 

oxidation 429 

Fault  (in  land-structure)  .     .  513-514 

Fauna  (animals) 530 

Ferrel's  Law 219 

Fertility  (of  soils)    ....  308-315 

causes  of 308 

Fertilizers  (of  soils)      .    315-319,  345 

Fertilizing  (of  flowers)      .     334,  390- 

392, 405 

Field  of  force  (of  magnets)     476-477 
Filaments      (of      incandescent 

lamps) >.     .     .     487 

Filters 143 

Fingal's  Cave  (wave-erosion)     .     160 
Fire  (caused  by  earthquakes)    .     515 

Fire-control 77-80 

Fire-extinguishment    ....       94 
Fishes  (vertebrates)     .    400, 533-534 

carnivorous 533^534 

Flood  basins 338 

Flood  plains  .     .     .          181-182, 185 

Flood  tide 164 

Flooding  (in  irrigation)    330-331,  346 

Flora  (plants) 530 

Flowers  (of  plants).     .    387-392,422 

colors  of 390 

extraneous  means  of  fertiliz- 
ing        390-392 

function  of 387 

scents  of 390 

seed  dispersal  of       ....     392 

structure  of 387 

Foci  (of  axis) 26 

Fog 104 

Food     .     .     .  303,313-314,373,383, 

398-421,  423,  425^41,  445- 

448, 451-457,  536 

absorption  of 421 

alcohol  and  tobacco  vs.     .     .     457 


Food  —  Continued 

bacteria  in       .       435-439, 445-449 

beverages 427,430, 

431-432,  446-448 

classes  of,  fundamental      .     .     425 

carbohydrates.     .     .      383,423, 

425-428,  456 

fats  and  oils      423,  425-429, 456 

proteins  .    383,  423,  425-429, 456 

composition  of     ....  426,  456 

conservation  of    ....  440-441 

cooking  and   preparation   of 

433-434,  457 

decay  of 303,438 

diet,  balanced 431 

disease  caused  by     .     .      445-447, 
452-455 

energy  through    .     .     .      399,419, 
428,  430,  456 

health  vs 425-433 

life  dependent  on     .    419, 425-426 

chlorophyll  in  leaves       382-383, 

399,  400,  419,  42.5-426 

minerals  in 430 

pasteurization 447 

storage  of,  by  animals  .     .     .     536 
tissue-making  and  tissue-re- 
pair by    313-314 

varieties  of : 

animal  (eggs,  meats,  milk, 

etc.)     .     .      427^30,446-447 
vegetable       (grains       and 
cereals,      fruits,      mush- 
rooms, nuts,  roots)     313,  373, 
398-399,    419,    425-426, 
430-431,  435,  437-438 
vitamins  (vital  element  of  life 
in  food)  ....    430-431,456 

water  vs 428 

Force  (attraction)  .     .  43-49,  58,  93, 
326, 476-477 

centrifugal 43-47 

centripetal    (gravitation   and 

gravity)  .      .      47-49,  58,  93,  326 

magnetic 476-477 

Forestry 339-345 

abuses  of  forests  .  .  .  340-344 
conservation  of  forests  .  344-345 
uses  of  forests  ....  339-341 


INDEX 


References  are  to  pages 


Formaldehyde  (disinfectant)  .  445 
Formalin  (disinfectant)  .  .  .  445 
Fossils  (of  animals  and  plants)  . 

522-523 
Franklin,  Benjamin  (inventor  of 

lightning-rod) 483 

Freeze  (southern  "  cold  wave  ")     228 

Friction      ....     63,72,462,480 

generator  of  electricity      .     .     480 

generator  of  heat     ...      63,  72 

methods  of  lessening     .     .     .     462 

Frost 104 

Fruits 427-431 

vitamin  in 431 

Fuel-saving 74-77,94 

Fulcrum  (of  lever) 464 

Fungi  ....  398-399,438-439 
a  cause  of  ptomaines  .  .  .  439 
mushrooms  and  toadstools  398—399 

Gala'pagos    Islands    (home    of 

great  tortoise) 541 

Galile'o  (inventor  of  lift  pump)     118 

Gases 2,17,42,58,97, 

110,115,315,472,504 
equality  of  pressure  of  .  .  .  115 
formation  of,  in  soil  .  .  .  315 
formation  of,  in  volcanic 

eruptions 504 

incandescent,  of  the  sun    .     .  2, 16 

inert 97 

transformers  of  energy      .     .     472 

Gasoline 105,140,520 

Gastric  juice 420, 433 

Geometry  (developed  by  Egyp- 
tians)      21 

Germination  of  seeds  .  .  .  393-396 
Germs  (harmful  bacteria) ;  see 

Bacteria 
Geysers  (hot  springs)       .     .511-513 

causes  of 511 

effects  of 513 

times  of  spouting     .     .     .     .     512 
Gibraltar  (a  spit)    ....  161-162 

Glaciers 285-301, 

304-305,  525-528 
Alpine  or  valley  ....  288-289 

crevasse' 289 

glacial  flour 291 


Glaciers  —  Continued 

glacial  formations    .     .     .  279-300 

glacial  lakes 300-301 

Glacial  Period      .     .  285,292-298, 
525-528 
effects   upon   animals   and 

plants 525-528' 

effects  upon  surface  285,  292-298 

glacial  scratches 291 

icebergs 294-295 

ice  fields  (of  Antarctic  regions 

and  Greenland)  .  .  .  293-294 
moraines  ....  290,297-300 
waterfalls  (Niagara  and  Yo- 

semite) 526-528 

Glass  (reflector  of  light)  .     .  348-349 

Globigeri'na 532 

Gneiss  (metamorphic  rock)       .     255 

Gold  (mineral) 516 

Graded  rivers 185 

Grafting  (method  of  plant-prop- 
agation)       377 

Grains  and  cereals      .     .     .  l'J7   >:H 
composition  of     .     .     .     .  42s  4:<1 
Granite  (igneous  rock)     .     .     .     253 
Grape     sugar     (developed     in 

plant-leaves) 382 

Graphite    (conductor    of    elec- 
tricity)   490 

Graphs 213-214 

Gravel 310,  345 

Gravitation  (attraction)   .     .     47, 49, 
58, 93,  :<LV, 

laws  of 47.58 

Newton's  discoveries     .     .       47 

Gravity  (earth-attraction)  47-48,  326 

vs.  soil-water .     .     .     .     .     .     326 

weight 47 

influences  upon  direction   .       4th 

Ground-water 170 

Gulf  Stream 162-164 

influence  upon  climates     .  162-164 

Hamoglobin  (of  blood)    ...    411 

Hail -W 

Halley's  Comet 18 

Halos 360,306 

Hammerfest's     climate     (Gulf 
Stream) 104 


10 


EVERYDAY   SCIENCE 


References  are  to  pages 


Harbors 188, 548-552 

advantages  of       .     .     .     .548-552 

necessity  of 548-549 

of  atolls 549 

of  deltas 549 

of  depressed  coasts  ....     549 

of  sand  reefs  and  spits       .     .     549 

of  submerged  craters    .     .     .     549 

Health  and  sanitation      99, 107-108, 

112-114,     120,     133,     202-203, 

361-362,  401,  408,  421,433,  439, 

441-457 

antitoxins  of  the  blood      .     .     444 
artificial    development    of, 

as  prophylactics    .     .     .     444 

bacteria  vs.     ...   120,  361-362, 

401,441-449 

conservation  of 457 

corpuscles,  white,  as  disease- 
fighters   444 

effects  of  dry  and  moist  cli- 
mates upon 108 

humidifiers 107-108 

food  and  its  preparation  vs. 

433-434 

laws  of 421 

ptomaines  vs 439 

sanitation  of  homes  and  sur- 
roundings    .     .     .      202-208, 
361-362,  443^57 

cleanliness 451-457 

disinfection        361-362, 443-445 
i    sewage  disposal    .     .     .  449-451 
water-systems      of      city- 
supply      .      202-208, 447-449 
throatal  adenoids  vs.    ...     408 

toxins  vs 444 

ventilation      .     .   99,112-114,133 
Hearing  ;  see  Ear ;  Sound 
Heart  (engine  of  body)     .     .  409-413 

composition  of 412 

function  of 412-413 

shape  of 412 

structure  of 412 

Heat     ....     2-3,16,18,28-31, 

60-95,    98,    107,    110,    124-127, 

136-139,  209-215,  221,  347, 

350-353,  357,  429-431,  480, 

486-487,  503 


Heat  —  Continued 

adiabatic 125,  221 

air  as  conductor  of  ...  107,  215 
properties  of,   vs.   heating 

systems 110 

animal  and  plant  life  affected 

by  ....  62,98,347,508 
boiling  in  different  altitudes  127 
capacity  of  water  to  hold  .  139 
compression  of  air  vs.  .  .  .  124 
conduction  of  ...  87-88, 94 
conservation  of  64,  90-94,  209-210 
contraction  by  ...  65-69, 94 
convection  currents  of .  88-90,  94 

density  vs 66, 94 

electricity  as  generator  of       .     62, 
486-487 

energy  generated  by     .     .     60, 93, 
137,  429 

expansion  of  air  vs.  ...  107 
factors  in  ....  211-213,429 

insolation  of 209 

intensity  of 350 

latent  heat 84-86 

light  transformed  into  .  .  347,  357 
magnetism  affected  by  .  .  480 

mass  vs 66,  94 

measure  of  ....  80-84, 94 
molecular  movements  in  .  67,  94 
production  of  ...  69-72, 94 

radiation  of 90 

reflection  of 351-352 

transmittance  of       ...  209-210 

water  vs 136-138 

absorbed  in 138 

evaporated  by      ....     139 

Heat  lightning 230 

Heavens,  the 1-19 

Hills ;  see  Mountains 

Honey  of  bees 405 

Honeycomb 405 

Horizon 355 

"  Hot  Wind  "  of  Texas    ...     229 
Household     ....   117-125,146, 
254-255,  307,  516-519 
appliances.     .       117-125,486-488 
bacteria  in  relation  to  forma- 
tion of  coal  and  peat     .516-517 
borax  as  aid  to  emulsion  .     .     146 


INDEX 


11 


References  are  to  pages 


Household  —  Continued 

building-material  and  cloth- 
ing       307 

homes  dependent  upon  soil   .     307 
minerals  and  mineral  oils    254—255,' 
516-519 
see  also  Sanitation 

Humidifiers 107-108 

Humidity 102-107, 133 

absolute  humidity    ....     102 

causes  of 104 

comfort  vs 106-107 

dew-point 102-104 

hygrometer 103 

relative  humidity     ....     102 
'  saturation 102 

Humors  (of  eye) 414 

aqueous 414 

vitreous 414 

Humus  (constituent  of  soil)      .    311, 
314-320,  327,  345 

bacteria  in       .....  314-315 
qualities  of 319-320 

Hydrogen  (a  gas)    ...      136, 167, 
425, 484-485 

constituent  of  food  ....     456 
constituent  of  water     .     .  136, 167 
formed  in  voltaic  cell  by  elec- 
tricity      484^85 

Hydrogen       peroxide       (disin- 
fectant)        444 

Hydrometer 153 

Hygrometer 103-104 

Ice    .          ...     127,137-138,279, 
285-287,  293-295, 303 
a    factor   in    earth's   surface 

changes 303 

contraction  of,   after  forma- 
tion     138 

erosion  by 285 

expansion  of,  while  forming  . 

formation  of 137-138 

glaciers,      icebergs      and      ice 
fields  285-301,304-305.525-528 

manufacture  of 127 

power  of 279 

pressure  of 1 

weight  of 138 


Illumination  ;    see  Light 
Imperial  Valley  (fertility  of)      -     173 
Incandescent  lamps     .     ...    488 
Incidence  (angle  of)     ....     352 

law  of 352 

Inclination  (of  axis)      ....       26 

Industries 546-547 

Inertia 42-49, 58 

laws  of 43,  44,  48. 49 

Influenza  (bacterial  disease)  .  442 
Inorganic  matter  (or  substance)  426 
Insects  (invertebrates)  400-405,  533 

beneficent 403-405 

productive 403-405 

bee 403-^05 

silkworm 403 

harmful 403 

of  the  sea 533 

of  the  soil 403 

Insolation 209-210 

Intakes  (cribs) 204 

Intensity 349-350,477 

of  heat 350 

law  of 350 

of  light 349-350. 477 

law  of 477 

of  magnetism 477 

of  sound 477 

International  Date  Line  .     .      :i.V  in 

Intestines 42O-421 

large 421 

small 4-Jo   l_'l 

function  of 421 

liver l-'l 

pancreas 4'J1 

Inventions      .        89, 91-92, 108-107, 

111,    117-131.    i:{7,    H:i,    147-150. 

202-206,    416,  459-474,467-478. 

483, 486-501 

Invertebrates      .     . 

400-1" 

inlets    .     .     .       400-405. 
protozoa     .     .      400-401,423,452 

shellfish 

worms    .     .    317-319,345.401-402 

Iris  (of  eye) 

Iron  and  steel  (niuKiu-t-nrnkinjc 

minerals) >7" 

Irrigation 33o 


12 


EVERYDAY   SCIENCE 


References  are  to  pages 


Irrigation  —  Continued 

ditching 331 

flooding      ....    330-331,346 

evaporation 331 

Islands      .     .     .      256,261,540-541 

continental 256, 540 

oceanic 540 

tropical 540 

variations  of  life-forms  on    540-54 1 

Isobars 214 

Isothermic  maps     ....  213-214 

Isotherms 213 

Isthmus  (of  land) 525 

Jupiter  (a  planet)    .     .     .   11-13,353 

brilliancy  of 12 

day  on 12 

distance  from  earth  and  sun  11 

eclipses  of  moons  of      ...  353 

size  of 13 

surface  of 11 

Kerosene  (mineral  oil)     .     .     .     520 
Kindling  temperature .     .     72-73, 94 
methods    of    bringing    sub- 
stances to 73 

spontaneous  combustion  .     .       73 
variation  of,  in  different  sub- 
stances     72 

Kinetic  energy    .     .     .     .60,  93, 396 

Lagoons 259-260 

Lakes   ....     171-174, 177-178, 
185,  300-301 

as  filters 172 

as  reservoirs 172 

evaporation  the  cause  of  salt 

lakes 172-173 

fringing  lakes 185 

glacial  lakes 300-301 

outlets  of 172-173 

Land     .     .     .  160-162, 175-176,  181- 

190,  247-306, 308,  525,  535-552 

bars,  sand  ....    162,  258,  282 

beaches 161,  251 

capes 258 

cliffs 160 

composition  of       252-255,  275,  308 
continental  shelf       .     .     .  256-259 


Land  —  Continued 

continents  ....    248,  256-276 

divides 175-176 

drowned  river  valleys  .     .  188-189 
dunes,  sand     .       258-259,  283-284 

hemispheres 537-538 

hills 264-265 

islands   .     .     .       256,261,540-541 

isthmus 525 

life  on    .     .     .       257-263,535-552 

marshes 260 

mountains  .     .     .     .      22, 238-241, 

248, 264-267,  541-543 

plains     .     .  181-185,  257,  268-276, 

301-302,  544-548,  553 

reefs,  sand 257-260 

spits 161-162 

structure  of 255-256 

terraces 186 

Latent  energy     .     .     .     .60, 93, 396 

Latitude 32 

Latitudes,  horse 221 

Lava  (volcanic  eruption)       .  277,  506 

Leaves  (of  plants)    379-386,421-422 

arrangement  on  stem    .     .  379-380 

regulation  of  sunlight    .     .     380 

composition  of     ....  382-383 

function  of 382 

shapes  of 380-381 

sun's  action  upon     ....     384 

veins  of 381 

water  in 385 

Lens  (of  eye) 414-416 

Lenses 355-356 

concave 355 

convex 356 

use  of 355 

Levees 184,  338 

Lever 462-465 

law  of 464 

law  of  machines 465 

principle  of 464-465 

Life   (common  to  animals  and 
plants)   .     .     .        98-100,135,141, 
151-152,    210,    257-263,    311-319, 
345, 347, 366-458i  522-553 
adaptability  to  physical  con- 
ditions    ....    528-535,552 
ancient  history  of    ...  522-523 


INDEX 


13 


References 
Life  —  Continued 

composition  of 366 

dependence  upon : 

air      ...     .98-100,141,152, 
210,313,425 

earth 366 

heat 347 

light 347,364 

soil-elements    .     .     .     .302,311 

sun 366,  384 

water  ....  135,311,425 
development  of  forms  of 

522-523, 539-540,  552 
differentials    as    to    animals 

and  plants 366 

distribution  of     ...      524-525, 

537-541,  552 

effects  of : 

climatic  changes  ....     525 
Glacial  Period       .     .     .  525-526 
physical    features    of   sur- 
face    .     .       277-278,523-524 
water      .     .       151-152, 166-167 

of  ocean 166-167 

embryo  of  ....    388-389,  394 
fertilizer  of  soil,  as  ....     318 

food,  as  419 

necessary  for  .  .  313-314, 366 
growth  of  ....  151-152,366 
man  in  relation  to  other 

forms  of 425 

microscopic,      necessary     to 

other  life 311 

of  the  land      .     257-263, 535-544, 

552 

of  the  ocean    .     .     .    531-535,552 

of  the  soil 311-319,345, 

401-402,  535 

phosphorescence  of  ...  533-534 
physical  conditions  of  earth 

vs 522-553 

powers  of 366 

propagation    and    reproduc- 
tion        366,524-525 

similarity  in  low  forms      .  399-400 

Light     ....     2-9,16,18,37,40, 

60-62, 93,  209, 347-365, 

486-187, 533-534 

color  .    356-364,390 


are  to  pages 

Light  —  Continued 

comfort  vs 361 

conservation  "of  .  .  .  37, 40,  362 
direction  of  movement  of  347-349 

disease  vs 361-362 

electricity     a    generator    of 

487-488, 601 

energy  generated  by      .     .     61, 93, 
357,501 

essential  to  life  ....  347.  364 
intensity  of  ...  349-350, 364 
moon  as  chief  source  of,  at 

night 16,349,351 

properties  of 348 

reflection  of  348-349,351-352,364 
refraction  of  .  .  .  353-356,364 

spectroscope 358,364 

spectrum  ....  357-358,364 
speed  of  ....  352-353, 364 
stars  as  lesser  lights  at  night 

I  0,847 

sun  as  chief  source  of  .     .  2-3,  18, 
60. 93, 347.  364 
artificial  lighting  .    347,  :,> 
moon  and  stars  as  lesser 
lights  .     .     .  4-9,  16,  347,  349. 
351 

theories  of  Newton  as  to  .     .     361 
Lightning  (electricity  in)       .     .     -Is:* 

lightning  rods 483 

Limestone  (sedimentary  rock)  .     254 

Liquids 42,58 

Lisbon  (earthquake  and  ocean- 
wave)     514 

Listerine  (disinfectant)     .     .     .     445 
Litmus  paper  (in  acid  and  alkali 

tests) 54-55,58 

Liver 

Loadstones    .     .     .     37-40.475-480 

attraction  of 476-477 

field  of  force   .     .     .'    .     .476-477 
intensity  of  attraction  .     .     477 

poles  of 39,40,476 

,am 309-310.345 

Local  soil  (mli-ntary)       ...     307 
ss  beds  (deposition)  ...    285 

Longitude •'<'-' 

Looming  (niiruw)   ... 
Loss  of  energy  "  .     .      63, 462-403 


14 


EVERYDAY  SCIENCE 


References  are  to  pages 


Loss  of  energy —  Continued 

friction 63,  462-463 

methods  of  lessening  63,  462-463 

Lubricating  oils 520 

Luminous  bodies  (light  from)   .     348 

Lungs 407-409 

air  sacks 408 

air  tubes 408 

arteries,  capillaries,  veins       .     409 
Lysol  (disinfectant)      .     .     .  444-445 

Machines 462-465 

law  of 465 

Maelstrom  (whirlpool)     ...     165 
Magnetism    .     .  37-39,  475-480,  501 

attraction  of 476 

compass      .     .     .   39,476-478,501 

field  of  force 476-477 

intensity  of  attraction .     .     .     477 
iron  and  steel  as  media  for 

magnets 476 

loadstones  .     .     .     37-40, 475-480 

magnets.     .     .     37-40,476-480 

molecular  theory  as  to      .  478-480 

properties  of 479-480 

Magnets ;  see  Loadstones 

Malaria  (protozoan  disease)  401,452 

Mammals 400,533 

Man  (vertebrate ;  mammal) 

166, 277-278,  303,  313-314,  373, 
383,  398-458,  523-553 

history  of 522-523 

structure  and  functions  of : 
organs : 
of  sense : 

ear,  of  hearing  416-418,  423 
eye,  of  sight  .  414-416,  423 
nose,  of  smell  .  .  413,  423 
skin,  of  touch  .  .  413,  423 
tongue,  of  taste  .  413,  423 
of  vital  functions : 

brain,   seat  of   nerve- 
communication  .     .     418 
heart,  engine  of  body 

409-413 
lungs,     blood-purifiers 

of  body      .     .     .  407-409 
stomach,    digester    of 
body 420 


Man  —  Continued 

skeleton 405-407 

appendages,   ribs,   skull, 

spine 406-407 

cavities  within : 

abdomen 410 

thorax 409 

systems : 

of  breathing      .    407-410,  423 
of   circulation   of    blood 

410-413,  423 
of  communication  (nerv- 
ous system)   .    413-418,423 
of  digestion  .     .    419-421,423 


muscles,  of  locomotion    .     407 
nerves,    of    sense-trans- 
mission     .     .    407,413-423 
Manures  (fertilizers)   .     .     .  316,  334 
Marble  (metamorphic  rock)      .     255 
Mars  (a  planet)       ....      11-13 

brilliancy  of 12-13 

day  on 12 

distance  from  earth  and  sun         1 1 

Marshes 260 

Marsupials  (vertebrate  pouch- 
animals)      538-539 

Mass 66,  94 

Matter  42-59,  67,  310-314, 475-501 
chemical  changes  of  .  .  53, 58 
chemical  compounds  of  .  53-58 
chemical  mixtures  of  .  53-54,  58 
classes  of : 

inorganic  (mineral)   .     .  310-311 

organic    . 314 

composition  of     ...    42, 49-52, 

58, 67,  500-501 

molecules     .     .   49-50,51,58,67 

atoms 50-51,58 

electrons  ....  500-501 
compounds  of  ...  51—52, 58 
elements  of  ....  51-52, 58 

energy  latent  in 57 

forms  of : 

.     .    2,17,42,58,97, 
110,115,315,472,504 

42,58 

42,58 

....     53-54,58 


liquids     . 
solids 
mixtures  of 


INDEX 


15 


Matter  —  Continued 

neutralization   of   acids   and 

bases 55-5' 

physical  changes  of  .  .  52-53, 5J 
planetary  movements  .  48-49,  5} 
properties  of : 

centrifugal  force  .     .     .      43^47 
gravitation 4 

electricity  and  magnetism 

475-50 

extension     ....     42-43,58 

inertia 42-47,58 

weight  of 47-48 

Meanders      ....    181-183, 187 
intrenched 187, 207 


Meat 


References  are  to  pages 

Milky  Way  (stars)       ....         5 
Mineral  matter  in  soil      .     .310-311 

Minerals 515-520 

Mining      .     .     .      515-521.542-543 
chief  industry   of   mountain 

regions 542-543 

of  coal 254, 516-519 

of  copper 516 

of  gold 516 

of  iron 516 

of  peat 309, 517-518 

of  petroleum 519-520 

of  silver 516 

regions  of 516 

veins  of  minerals      ....     515 


427-429 


as  food 427 

oxidation  of 429 

protein  in 427-129 

quantity  required  in  diet  .  .  428 
Media  (of  light)  ....  354-355 
Mercury  (a  planet)  .  .  .  11-13 


day  on 
distance  from  e; 
orbit  of  ... 
position  of 
temperature  of 


irth  and  sun . 


Meridians  and  parallels  30-37,  39-40 
degrees,  minutes,  seconds  .  32 
International  Date  Line  .  35, 40 
latitude  and  longitude  ...  32 
measurement  of  time  .  .  32-37 

Prime  Meridian 32 

Standard  Time  .  .  .  34-35, 40 
daylight  saving  ...  37, 40 
time  meridians  of  ...  35 

Mesas 272,  276 

Meteorites 11 

Meteors 11 

heat  of 11 

light  of 11 


Mica-schist 255 

Microbes 98 

Microscope 356 

Midnight 33 

Milk     ....      427,430,446-447 
a  balanced  food  ....  427-430 

constituents  of 430 

dangers  from  infected  .     .  446-447 


Mirage  (looming) 


366,860 


cause  of 355 

Moisture  (water-vapor)   .      100-107, 
112, 141,280,303,535 
a     factor     in     atmospheric 

weathering 280 

a  factor  in  development  of 

bacteria,  molds,  yeasts  .     .     303 
a  factor  in  life  of  animals  and 

plants 535 

in  air 100-107,141 

Molds 303,399.422 

spores 399 

Molecules  (of  matter)      .    49-59,  67, 
94, 478-480.  500-501 

atoms 50-51,58 

electrons 500-501 

changes  in 53, 58 

compounds  ....  54-55,68 
neutralization  .  .  55-56, 58-59 
...  67.94 
i  magnot- 
.  .  .  478-480 
.  .  .  375-377 
....  375 
....  15 
.2.4.14-17,19, 


energy  in    ... 
molecular  theory 


Monocotyledons 

structure  of 
flonth  (origin  of) 
Moon,  earth's     . 

165.  210.  347-351 

a  source  of  reflected  light     16. 347. 
MB,  IS] 

axis  of    ........        15 

day  and  night  on     ...      15.  17 

diameter  of 1* 

distance  from  earth  and  sun  15, 19 


16 


EVERYDAY  SCIENCE 


References  are  to  pages 


Moon,  earth's  —  Continued 

eclipses 16-17, 19 

heat  of 16 

light  from  .     .     .16,  347,  349,  351 

orbit  of 15 

phases  of 16,  19,  349 

revolution  of  ....     15-16, 19 

rotation  of 15 

size  of 2 

surface  of 14-15 

tides  influenced  by  .     .   17, 19, 165 

weight  of 15 

without  atmosphere  or  water     210 
Moons  (satellites)   ....      11-19 

Moraines 290,  297 

ground 297 

lateral 290 

medial 290 

terminal 290,298 

Morse,  Samuel  F.  B.  .     .     .  492,  494 

Mosquitoes    ....    403,452-454 

Mountains      .     .     .22,238-241,248, 

264-267,  541-543 

age  of,  old  and  young  .  .  266-267 
effects  of,  upon  climate  .  238-241 
effects  of,  upon  history  .  541-543 

hills 264-265 

mining    the    chief    industry 

of 542-543 

peaks  of 266-267 

products     of     recent     earth- 
changes  248 

ranges  of 267 

structure  of 265-266 

volcanoes    ....    503-511,521 

Mouth 408, 420, 423 

esophagus  (throat)  ....     408 

epiglottis 408 

saliva 420,433 

teeth 420 

Moving  pictures 416 

Mulches 328 

Muscles 407 

Mushrooms 398-399 

spores 399 


Neap  tide  .     .     .     . 

Neptune  (a  planet) 

day  on  .     .     .     . 


.  .  .  165 
5,11-13,49 
.  .  .  12 


Neptune  (a  planet)  —  Continued 
discovered  by  laws  of  gravita- 
tion and  inertia    ....       49 
distance  from  earth  and  sun    5,  11 

moons  of 13 

orbit  of 12-13 

Nerves    (transmitters    of    im- 
pulses and  sensations)  .     .  413-423 

of  hearing 416-418 

of  sight 414-416 

of  smell 413 

of  taste 413 

of  touch 413-414 

Nervous  system        407,  413-418, 423 
brain  as  seat  of   .     .    407, 418, 423 

nerves 413-418 

spinal  cord 407 

Neutralization    (of    acids    and 
bases) 55-59,315 

Newton,  Sir  Isaac  ....     43-44, 

47-49,  58,  361 

Newton's  First  Law      .     .      43-44 

on  gravitation 47 

on  light 361 

Niagara  Falls  and  River  .     .  177,  526 

Nitrogen  (a  gas)      .     .       52, 97-100, 
133,311-314,345,425 

an  element 52 

compounded  for  use  ...  99 
constituent  of  air  ...  97-100 
necessary  for  life  .  .  .313-314 
constituent  of  food  .  .  425,  456 
necessary  for  soil  .  .  .310-314 

North  Star  (Polaris)     .     .       9-10, 24 

"  Northern    Lights "     (Aurora 
Borealis) 360 

Nose  (organ  of  smell)       .     .  413,  423 

Obsidian  (igneous  rock)  .     .     .     253 

Ocean  .     .  17, 19, 152-169,  213,  249- 

25 1 , 256-258, 514, 53 1-535, 552 

composition  of  water  of    .  152-154 

currents  in       ...     161-164,  169 

effects  of      .     .     .     162-164,213 

motion  of 162 

rotating  surface  of     .     .     .     162 

sargasso  seas 162 

density  of 154,  168 

depth  of 154, 168 


INDEX 


17 


References  are  to  pages 


Ocean  —  Continued 

floor  of 155-156, 168 

heat  vs.  distance  from  .  .  .  213 
land  interchanges  with  .  249-251 
life  in  and  of  ...  531-535,  552 
pressure  in  ...  154-155, 168 
swell  below  surface  of  .  .  .  155 
temperature  of  water  of  156-157, 
168 

tides  of  ...  17, 19, 164-166, 169 
value  of,  to  man  and  other 

life 166-169 

volume  of  air  in  water  of  .     .     155 

waves 157-161, 169 

"  Oil  on  water  " 158 

Ooze  (of  ocean-floor)  ....     156 

Optic  nerve 414 

Orbits  (of  planets)  ...  12,  26-31 
Organic  matter  (or  substance)  .  426 
Osmosis  (diffusion  through 

membrane) 371 

Ovary  (of  flower) 387 

Oxbow  lakes 182,184 

Oxidation 429 

Oxygen  (a  gas)    ....       97-100, 

132-133,  136,  141,  152,  167,  280, 

399-400,  410, 413, 425, 456 

a  constituent  of  air  .     .     .  97-100, 

132-133 

a  constituent  of  water  .  .  136, 167 
agent  of  combustion  ...  98 
agent  of  weathering  .  .  .  280 
constituent  of  food  ....  456 
necessary  for  life  .  .  98,  141, 
152,410,413 

Pancreas 421 

Parallels;     see  Meridians  and 
parallels 

Parasites 397-400 

Passes     (in    mountainous    re- 
gions)      176 

Pasteurization  (of  milk)  .     .     .     447 

Peat 309,517-518 

Peroxide    of    hydrogen    (disin- 
fectant)        444-445 

Perspiration 1("> 

Petrified  trees 522-523 

Petroleum 519-520 


Phosphate  rock  (as  fertilizer)    .     317 
Phosphorescence    ....  533-534 

light-emission      by      micro- 
scopic animals     ....     633 

Phosphoric  acid  (as  fertilizer)  .     316 

Phosphorus  (as  fertilizer)      .  <)7,  311. 

316,345 

ignition  qualities  of      ...       97 
necessary  for  soil      .     .     .     .     311 

Photography      (utilization      of 
principles  of  light-refraction 
and  magnifying)       ....     356 

Physical  changes  (in  matter)     53,  58 

Physical  features  (of  earth)     541-552 

effects  upon  life  ....  541-552 

Piston  (of  engine)   .....     471 

Pith  rays  ........     374 

Plains  .     .        181-182,  185,  257-259, 
268-276,  285,  301-302,  544-548,  553 
coastal  .....    257-259,274 

effects  of  life  on  .     .    544-548,  553 
flood      .....    181-lN-'.  IV, 

Great  Plains  of  U.S.      .     273-275, 
276 

prairies  .     .      274,285,301-302 
plateaus      ....    268-273.  -J7C, 

Planetary  movements      .     .      48-49 
laws  of  gravitation  and  in- 

ertia   .......       48 

discovery  of  Neptune  and 
Uranus  by    .....      49 

Planetary  wind  belts  ....     _'-':.' 

Planetoids  ;  sec  Asteroids 
Planets      .     .     .    4-15,  18-19,  20-21 
brilliancy  of  Jupiter,    Mare, 
Venus     .......        1- 

day  and  night  on     .     12-11.  I".  !'' 
development  of  science  con-    - 


distances  from   one  another 
and  -MI,  ......      11.  19 

distinguishing  features  of  .     .     4-5 
light  of  ......  4,.r>.  i:«.  I'.i 

reflected  rays  from    .     .      13-14 
moons  of    ....    11.14,15.19 

orbits  of      ......        I--  !'•' 

positions    ......      M    r.' 

revolutions      .     .     ,      6,12,18,18 
rotations    ......       1-'.  ''•' 


18 


EVERYDAY  SCIENCE 


References  are  to  pages 


Planets  —  Continued 

sizes  of  .     .     .     .     .     .     11,13,19 

solar  system 10-19 

surfaces  of 11 

temperatures  of  .     .     .     .      11, 19 

visibility  of 13 

Plants  .     .     .    98-100,  166,  279,  284, 

366-399, 419, 421-422, 424, 

425-427,  431,  435-441,  445-447, 

522-541 

bacteria      .     .      398-399,422,435 
cambium  layer    ....  374,  377 

capillary  action 372 

carnivorous  plants   .     .     .  380-381 

cells  of 371 

chlorophyll  in 397 

circulation  of  sap  in      ...     382 
classes  of : 

by  distribution : 

of  land    284, 535-536,  540-541 

of  sea  .     .     .     .     166, 531-532 

dependents.     .     .    397-399,422 

green-leaved  plants  .     .  397-399 

diastase 383 

energy  of 399 

factors  in  surface  changes      .     279 
food, as  373,  399, 419,  425-427, 431 

fossils  of 522 

growth  of 372 

molds 399, 422 

osmosis  in 372 

physical  conditions  vs.      .  522-541 

propagation  of     .     .  377, 392-393, 

398-399 

protoplasm  in 371 

self-protecting  plants    .     .     .     381 
structure  of : 

flowers  ....  387-392,422 
leaves  .  366,379-386,421-422 
roots  .  .  .  366-373, 421-422 
seeds  .  .  .  389,  392-396, 422 
stems  .  366,373-379,421-422 
yeasts  .  .  303,399,422,436-437 

Plasma 41] 

Plateaus 268-273,276 

dissected 270-271 

old 272-273 

young 268-269 

Pneumonia  (bacterial  disease)  .     442 


Polar  winds 220 

Polaris  ;  see  North  Star 
Poles : 

of  earth 8-9,  26 

of  magnets 476 

Pollen 388 

Pollen  basket  (of  bees)     ...     404 

Polyp,  coral 533 

Potash  (fertilizer) 317 

Potassium  (fertilizer)  .     .     .     .     316 
Potassium  (necessary  for  soil) 

311,345 

Potential  energy 396 

Power  (generated  by  combus- 
tion, running  water,  wind)  472-473 
Prairies  (of  U.  S.)    274,  285,  301-302 
Pressure    .     .     .      123-126, 146-147, 
154-155,  210-211,  502-503 

boiling-point  vs 125 

condensation  of  steam  vs.      .     126 

effects  of 502-503 

laws  of 123 

of  air 123,210-211 

of  water      .     .       146-147, 154-155 

transmission  of 147 

within  earth    .     .     .     .     .  502-503 
Prism   (separator  of   colors  of 

spectrum) 356-359 

Promontories 160 

Proteins : 

composition  of     .     .    383,  425, 427 
food  properties  of     ....     428 
amount  necessary  in  diet   .     428 
found  in  eggs,  fish,  milk, 

meat,  etc 427 

origin  of 425, 

required  for  growth  and  re- 
pair of  body-tissues  .     .     .     428 
Protoplasm  (life-principle)     383-384, 
400,  419,  425,  428-430 

composition  of 428 

developed     in     green     plant 
leaves       .  383-384,400,419,425 
428, 430 

Protozoa  (invertebrates)        400-401, 
452-455 

a  cause  of  disease     .    401,  452-457 

analogy  to  bacteria  ....     401 

Ptomaines  (caused  by  fungi)     .     439 


INDEX 


19 


References  are  to  pages 


Pulse 41 

Pupil  (of  eye) 41 

Radiation  (of  heat)      ....      9( 

Rain      .     104,  141,  170-174,  231-237 

241 

Rainbow 359,  365 

Rats  (carriers  of  disease)       .     .     454 
Reclamation  (of  soils)       .     .  332-338 

of  alkali  land 332-333 

of  arid  land 336-338 

of  overflowed  land   .     .     .  338-339 

Reefs,  sand 257-260 

Reflection  (angle  of)    ....     352 

law  of 352 

original  rays  of 352 

Refraction  (of  light)    .    353-356.  364 

cause  of 353-355 

effects  of 355 

Relishes 431 

Reptiles  (vertebrates)       .     .     .     40(1 
Repulsion  (of  magnets)    .     .     .     476 

Reservoirs 172,  201 

for  water-supply  of  cities  .     .     201 

lakes  as 172 

Respiration ;  see  Breathing 

Retina  (of  eye) 414,416 

Revolution  (of  earth)  .    26-31,39-40 

Rivers.     .     .     .       176-208,546-548 

as  inland  waterways     .     .  190-196 

improvement  of    ...  192-196 

classes  of    ....    181-190,207 

deltas      .     .      189-190,207,549 

drowned      .     .     .    188-189,207 

intermittent 186 

meanders     .      181-183,  187,  207 

terraced 186 

development  of    .     .   177-181, 186, 
207 

graded 178-181 

old-age    .     .     .     .     .     .  186, 207 

young     ....    177-178,207 

fall  line  of 547-548 

of  coastal  plains  ....  546-547 
Rocks   .     .     .    252-255,275,279-281 

igneous 252-253,  275 

metamorphic  .  .  .  254-255, 275 
sedimentary  .  .  .  253-254,275 
weathering  of  ....  279-281 


Roemer   on    deductions   as   to 
light 352-353 


Rolling  (of  soils) 
Roots  (of  plants) 

as  food 

functions  of    .... 

growth  of 

rise  of  sap  in  .... 

structure  of     .... 

uses  of 

Rotation  (of  earth)       .     . 

effects  of 

four  cardinal  directions 

inclination  of  axis    .     . 
Run-off  (of  water)  .     .     . 


327 

366-373, 421^422 

373 

....  373 
.  .  . 372-373 
....  372 
....  372 
.  .  .  367-371 


.   24 
24.39 


174 


Saliva 420,433 

Salt 142, 425 

necessary  for  life-processes    .     142 

solutions  of 142 

Salt  Lakes 172-173 

causes  of 172 

fertility  of  beds  of    .     .     .     .     17:( 
Saltpeter  (as  fertilizer)     ...     316 

Salts 54,58 

obtained  by  neutralization  of 

acids  and  bases     .     .     .      54, 58 
San  Francisco  (earthquake  and 

conflagration) 515 

Sand     .     .     .162,281-285,307-310, 
319-320. 345, 549 
an  agent  in  surface-changes 

281-285 

deposition  of 283-285 

Sand  blasts 281 

Sandstones  (sedimentary  rock) 

253-254 
Sandy  soils    .     .     .     .307. 
Sanitation  ;  *rr  Health  and  wiiiit:iii<ni 
Santa  Ana  (cyclonic  storm) .     .     -:.'!» 

Sap  (in  plants) 372 

Saprophytes     (dependents     on 
dead  animals  and  plants)       .     397 

Sargasso  seas 162.532 

Sargassum  (sea-plant)      .     .     .     532 

Satellites ;  tee  Moons 

Saturation  102-103,  104, 106,  112, 141 

in  solutions     .....      141 

in  air      102-103,  104,  106,  ll-'l  n 


20 


EVERYDAY  SCIENCE 


References  are  to  pages 


Saturn  (a  planet)    ....      11-14 

day  on 12 

distance  from  earth  and  sun         11 

moons  of 11 

rings  of 13-14 

surface  of 11 

Scents  (of  flowers) 390 

Science,  earth  (development  of) 

8-9,  20-21 

Sea        ....       160,213,249-251 

beaches 251 

caves 160 

distance  from,  a  factor  in  heat     213 
interchange  with  land  .     .  249-251 

Seasons     27-31,40 

causes  of 27-31 

equinoxes,      autumnal      and 

vernal 31 

solstices,  summer  and  winter       30 

Seaweeds       ....    162,531-532 

sargassum 532 

sargasso  seas 162 

Seeds  (of  plants)    .     .     .      388-389, 

392-396,  422 

cotyledons.     ....       394,422 

development  of 395 

dispersal  of 392-393 

embryo 388-389,394 

energy  of 396 

germination  of     ....  393-394 

Seepage  (in  irrigation)     .     .     .     326 

Senses 413-418,423 

nerve-connection  with  brain  .     413 

of  hearing 416-418 

of  sight 414 

of  smell 413 

of  taste 413 

of  touch 413 

Sewage  (disposal  of)    ...  449-450 
see  also  Health  and  sanitation 

Shellfish  (invertebrates)  .     .     .     400 

Shells  (of  low-life  animals)  .     .     401 
chalk  cliffs  of  England      .     .     401 

"  Shooting-stars  ;  "  see  Meteors 

Shore    ....     243-244,256-259, 
540-541,549 

continental  shelf      .     .     .  256-259 
bars,  dunes,  islands, 
lagoons,  reef s  256-259,  540-541 


Shore  —  Continued 

depressed  coasts 549 

effects  upon,  of  sun  .  .  243-244 
Sight  (sense  of)  .  .  .  414-416,  423 
Silkworms  (productive  insects)  403 

Silt 309-310,321,345 

Silver  (mineral) 516 

Sirocco  (cyclonic  storm)  .     .     .     229 
Skeleton  (of  man)  ....  405-406 

appendages 406 

ribs 406 

skull 406 

spine  (vertebral  column)  .  .  406 
Skin  (organ  of  touch)  .  .  413,  423 
Sky  (the  heavens)  ....  1-19 

"  Slack  water  " 164 

Slate  (metamorphic  rock)     .     .     255 
Sleeping  sickness,  African  (pro- 
tozoan disease)    .     .     .     .401,452 

Sleet 104,  234 

Smell  (sense  of) 413 

Snow 104,  234 

Soap  (emulsifier)     ....  145,  445 

Soils      ...    57, 173, 197-198,  209, 

212-213,  284-286,  293-300, 

307-346,  401-403,  534 

agricultural     .     .     .    313-341,345 

building-materials  dependent 

upon 307 

classes  of  .  284-285,307-310,345 
clothing  dependent  upon  .  .  307 
composition  of  .  .  308-326, 345 

cold  frame 209 

conservation  and  reclamation 

of  ....      322,332-339,345 

cultivation  of .     .     .    329,334,345 

drainage  of      ...  313,  323-326 

331-332,  334,  345 

evaporation  of  soil-water  327-329 
fertility  of  .  .  173,  308,  313,  315, 
317-319, 345, 401-402, 535 
fertilizers  ....  315-319,345 
food  dependent  upon  .  .  .  307 

forestry  vs 339-345 

formation  of  285-300,  307-310,  345 

heat  vs 212 

insects  vs 403 

life    (animal    and    plant)    in 

311-319,  345, 401-402,  535 


INDEX 


21 


References  are  I 
Soils  —  Continued 

bacteria,     beneficent     and 

harmful    .     .     .    314-318,345 
earthworms,    fertilizers    of 


317-319,  345, 401-402 
mulching  ....  328-329,345 
subsoil  ........  307-310 

surface  soil 308 

varieties  of    307-3 1 0,  3 1 9-32 1 ,  345 

ventilation  of 313 

water  vs.    .    311-312,319,321-326 

Solar  day 33 

Solar  family,  earth's ;  see  Solar 
systems 

Solar  systems : 

sun's 5,10-18 

stars' 6 

Solids   . 42, 58 

see  also  Matter 

Solstices  (summer  and  winter)        30 

Solutions 139-142 

in  water 142 

saturated 141 

with  salt 142 

Solvents  (alcohol,  gasoline,  tur- 
pentine, water) 140 


Sound 

wave-motion  .     .     . 

medium  of  hearing 

transmission  of     . 

ear,  organ  of     . 


.    416-418,423 
.     ...     417 
.     417 
.     418 
.     418 


Specific  density  of  water       .     .     150 

Specific  gravity 47 

Specific  heat .......      84 

Spectroscope       .     .     .     .     .  358, 364 

Spectrum 357-358,  364 

Spinal  cord 407 

Spine  (vertebral  column)      .     .     406 

Spits 161-162,549 

Gibraltar 161-162 

harbors  of 549 

Spores    (of   molds   and    mush- 
rooms)    399 

Springs  (cold  and  hot)     .     .     .     196 

Springtide 165 

Sprout  (of  plants) 394 

Stamens  (of  flowers)    ....     387 

Standard  time    ....     34-50,40 

daylight  saving   ....      37,  40 


Standard  time  —  Continued 

International  Date  Line  .  35, 49 
time  meridians  of  .  ..."  35 
variations  from  exact  time  .  34 


Starch   (a   carbohydrate)    382,  426- 
429 

Sta« 3-10,18-19,347 

constellations  of  .     .     .     .  9-10, 19 
distances  from  earth  and  sun 

6-8.18 
Arcturus,  light  from      .     .         7 

light  of 4-9, 347 

Milky  Way 5 

North  Star 9 

positions  of 5, 8. 9 

sizes  of 6 

suns,  as G,  18 

solar  systems 6 

Steel    and    iron    (as    magnet- 
making  minerals)     ....     476 
Stems  (of  plants)     373-379, 421-422 

buds  of 378 

functions  of 375 

propagation  on 377 

structure  of 373-377 

types  of 375, 422 

varieties  of 375 

Steppes  (of  Russia)  ....  286 
Stigma  (of  flowers)  ....  387 
Stock-yard  by-products  (as 

fertilizers) 316 

Stomach 420 

gastric  juice 420 

see  also  Digestion 
tomata  (of  plant-leaves)     .     .     386 

Storms 125,221-231 

adiabatic  cooling  and   heat- 
ing, a  cause  of      ....     125 

anti-cyclonic 224 

cyclonic      ....    221,226-231 
see  also  Winds 
Streams ;  see  Rivera 

Submarines 150-161 

Submergence     .     .     .    150-151,303 
a  factor  in  surface-changes    .     303 

in  water 160-151 

of  submarines  ....  160-151 

Subsoil 309. 

Substances ;  see  Matter 


22 


EVERYDAY  SCIENCE 


References  are  to  pages 


Sub-surface  water  ....  196-198 
Sugars  (carbohydrates)  382,  426-429 
Sulphur  (disinfectant)  .  .  .  445 
Summaries : 

air  and  atmosphere .     .     .  132-134 

earth 39-40 

energy 474 

heat 93-95 

life    (animals,    man,    plants) 

421-423, 456-457,  552-553 

light 364-365 

magnetism  and  electricity     .     509 

matter 49-51 

sky 18-19 

soils 345-346 

surface    (crust,    outside    and 
within)    .     .     275-276,304-305, 
530-621 

water  and  waterways  .      167-169, 
206-208 

weather  and  climate     .     .  244-246 

Sun,  our  .     .  1-19,  27-30,  60-95, 101, 

165,  209-210,  242,  248.  303, 

347,  350.  355,  360,  364-365, 

396. 399-400,  535 

appearance  of      .   2-1, 17,  360, 365 

incandescent  gases    .     .     .  2, 17 

corona     .     .     .      17,360.365 

spots  of 2-4 

atmosphere  as  cold  frame    209-2 10 

circumference  of 1 

composition  of 2 

diameter  of 2 

distance  from  earth      .     .      2, 350 
effects  of,  upon  earth's  sur- 
face      248.303 

upon  interior 248 

upon  exterior 303 

effects  of,  upon  life  ....     535 
evaporation  caused  by      .     .     101 

family  of 5-19 

influence  of,  upon  tides     .     .     165 

interior  of 2 

rays  of 28-30,242 

by  day  and  night      .     .      28-30 

by  seasons 28-30 

penetrating  land  and  water     242 

siieof 1-2.18 

solar  system 5, 10-18 


Sun  —  Continued 
source  of: 

clothing  .......        3 

energy     .....  3,399-400 

food   .......      3,399 

heat   ....       2-3,18,60-95 

life     .......    99,384 

of  animals    .....     384 

of  plants  .....    99,384 

light  .       2-3,18,60,93,347,364 
power      .......         3 

surface  of  .......         2 

transmitter  of  heat  and  light,  as  209 
volume  of  ......        2,  18 

Sundial    ........      33 

Sunlight  (as  disinfectant)      .     .     445 
Suns: 

our  sun  ;  see  Sun 
stars  ;  see  Stars 
Sunset.     .     ......  358,365 

Surface  (of  earth,  crust)  .     .     .    166, 
247-306,  502-553 

changes  in  .     .     249-252,  258-263, 
275-305.  523,  525-528 
by  burial  and  exhumation 

258-259,  282-284 

(through  wave  and  wind  action) 

by  decay  and  growth    .     .    -'7;). 

302-303,  305 

(through  animals  and  plants) 
by  deposition  and  erosion 


(through  volcanic,  water, 
wave  and  wind  action) 
by  depression  and  elevation    252 
(through        cruet-move- 
ment and  volcanic  ac- 
tion) 

by  emergence  and  submer- 
gence     260-263,  275,  303,  523 
(through  ocean  and  other 

water-bodies) 

by  ice  and  snow   .  279.  285-305, 
i 
by  interchange  of  land  and 

sea       ....    249-252,523 

by  rock-weathering  .      278-281, 

304-305 

characteristics  of,  252  .  -   -  JM   J  7  ii 


INDEX 


23 


References  are  to  pages 


Surface  —  Continued 

cycles  of  change       ....     303 
i  nterior  conditions  of,  249 , 502-52 1 
pressure   vs.    temperature 

502-503, 520-521 

volcanic  action     .     .     .  504-521 

earthquakes      .     .     .  513-515 

faults 514 

geysers     .     .     .    511-513,521 

islands 509-511 

volcanoes : 

distribution  of   .     .508-511 

Monte  Nuovo   504,506,521 

Mt.  Pelee       .    506-508,  521 

Vesuvius  .     .    504-506,521 

life  (of  animals,  man,  plants) 

in  relation  to    .     .   166,277-279, 

522-553 

mineral  deposits  of  ...  515-521 
coal,     copper,     gold,     iron, 
silver  ......  516-519 

peat 517-518 

petroleum  and  other  oils,  519-520 

veins  of  minerals  ....     515 

original  condition  of     247,  275,  278 

structure  of 255-274 

Suspension  of  matter  in  water  .     142 

Swamps 174 

Swarm  (tee-colony)     ....     404 
Swell  (in  ocean) 155 

Tantalum 488 

Taste  (sonse  of) 413 

Teeth 420 

Telegraph 492-494 

invented  by  Morse  .     .     .  492, 494 

key  of 493-494 

sounder 493-494 

wireless 495 

Telephone  ....'...    495 

Telescope  (lenses  of)   ....     :tf«i 

Temperature       ....    11.72-94. 

100-102,    106-109,    136-lMs.     1  I.'. 

156-157, 211-213, 227-228, 248. 281 

a  factor  in  surface-change*    .     '-'SI 

air  vs.    . 107-109 

evaporation  vs.     100-102.  IOC,   107 
graphic    method   of   showing 
records  of -'13 


Temperature  —  Continued 

heat  vs 72-94 

specific  heat 84 

measurement  of  ...     80-82, 94 

thermometers  .     .    80-82. 93-94 

of  ocean  waters   .     .    156-157,  213 

of  planets 11 

of  salt  solutions 142 

pressure  vs 136-^38. 

211-213,227-228. 2 
vs.  depth  within  earth  .  24h.  502 
vs.  distance  from  sea     .     .     213 

vs.  height 212 

vs.  latitude 211 

vs.  soil 212 

vs.  storms - 

vs.  water 136-138 

Terraces,  river 186 

Terrestrial  winds  .  .  .  .2.1.245 
Texas  fever  (bacterial  disease)  454 
Thermometer  .  .  .  80-82,93-94 

scales  of 81-82 

Centigrade  .     .     .    81-82, 93-94 
Fahrenheit  ....     82. 93-94 

formulae 93 

Thorax  (of  man)      ....  409-410 

Throat 408 

Thundersqualls ;    see  Thunder- 
storms 
Thunderstorms  .     . 

cause  of - 

Tick  (carrier  of  diwaw)   ...     454 
Tidei  (of  ocean)      .      17-19,  164-166 
eddiw,      tidal      undulation*, 

whirlpools 165 

Antwerp.  Hell  Cafe.  Marl- 
Strom  165 

ilitllirurr  of  IMIUUI   upon    17,  19,  165 

illllliriii-r  of  Mill  upon     .       . 

•'  *la.-k  water  "     .      .      .      . 

varietieH  of 1' 

flil.  tido 164.  166 

IU.,1  ti.lr 

neap  tide 165 

.sprint  tide 165 

Tillage;  .«•••  Cultivation 
Time     . 

Ill    InMIIMtl.Ml    .'I    r.Ulll 

International  l>at.-  l.inr    .       35,40 


24 


EVERYDAY  SCIENCE 


References  are  to  pages 


Time  —  Continued 
measure  of      .     . 

day  and  night . 

year   .... 
Standard  Time    . 

variations  from 


24-26,  33 
24-26,  33 
.  .  26 
34-35, 40 
34 


daylight  saving      .     .      37, 40 

time  meridians 35 

Toadstools 398 

Tobacco  (effects  of)     .    432-433,  456 
Tongue  (organ  of  taste)  .     .     .     413 

Tools 459-461 

development  of    ....  459^61 

primeval 459 

see  also  Inventions 
Tornadoes     (cyclonic     storms) 

230-231,  245 
Torricelli  (inventor  of  mercury 

tube) 118 

Touch  (sense  of) 413 

Toxins 444 

Trade  winds 221,  245 

Transference  (of  heat)  .  .  86-94 
conduction  ....  87-88,94 
convection  current  .  .  88-90, 94 

radiation 90,94 

Transmission    (of    water-pres- 
sure)        147 

Transpiration    (evaporation    in 

plants) 106 

Transportation 167, 196 

rivers  as  means  of    ....     196 
ocean  as  means  of    ....     167 

Tropical  calms 221 

Trough  (of  waves) 157 

Tsetse  ( carrier  of  disease)     .     .     452 
Tuberculosis  (bacterial  disease)     442 

Tungsten 488 

Turpentine  (a  solvent)     .     .     .     140 

Twilight 3,355 

Typhoid  fever  (bacterial  disease)    442 

Universe  (of  the  ancients)    .     .  8 
Uranus  (a  planet)   .     .     .     .      11,49 

day  on 12 

distance  from  earth  and  sun  11 
position  in  space  determined 
by  laws  of  gravitation  and 

inertia     ...  49 


Valves  (of  heart) 413 

Vaporizing  (of  water)  .     .     .     .     136 

Vegetables 427-431 

composition  of 430 

Veins  (filled  with  minerals)  .     .     515 

Veins  (of  leaves) 381 

of  dicotyledonous  plants  .     .     381 

of  monocotyledonous  plants  .     381 

Veins  (of  human  body)    .     .     .     409 

capillaries 409 

functions  of 409 

Ventilation     ....     112-114,313 

of  houses 112-114 

of  soils 313 

Ventricles  (of  heart)    ....     412 

Venus  (a  planet)     ....  5, 11-12 

beauty  and  brilliancy  of   .     .       12 

day  on 12 

distance  from  earth  and  sun       5,  12 

Vertebrates 400 

amphibia,  birds,  fishes,  mam- 
mals, reptiles 400 

Vesta  (an  asteroid)      ....       11 
Vesuvius  (a  volcano)  .     .     .  504-506 

Monte  Somma 506 

Herculaneum  and  Pompeii     506 

Vitamins 430-431,436 

effect  of  heat  upon  ....     430 

vital  element  of  food    .     .     .     430 

Volcanic  action  .     .     .   155,  284-285, 

503-515,  523 

earthquakes    .     .     .     .     .513-515 

fault 513-514 

geysers 511—513 

islands 509 

volcanoes    .    284-285,503-511,523 
Volcanoes  155,  284-285,  503-511, 523 

cause  of 503 

craters  of 503 

distribution  of     .     .  •   .     .  508-511 
eruptions  as  factors  in  sur- 
face-changes     .     .     .284-285 
eruptive  matter    .     .      284-285, 
504-506 

loess  beds 285 

famous  volcanoes     .     .     .  504-510 

Monte  Nuovo 504 

Mt.  Lassen       ....  509-510 
Mt.  Pelee 506-508 


INDEX 


25 


References  are  to  pages 


Volcanoes  —  Continued 

Vesuvius 504-50G 

on  ocean  floor 155 

Volta  (discoverer  of  voltaic  cell)     484 
Voltaic  cell  (in  electricity)    .     .     485 

Volume 66,94 

Vulcanite  (in  magnetism)      .     .     480 

Water  ....  98,100-107,127, 
135-169,  170,  174-179,  196-207, 
278,  311-313,  319,  324-327,  347, 
385,  400-101, 425,  445, 447-449, 528 

u  disinfectant 445 

a  food 428 

a  necessity  to  life-processes 

135, 425 
a  solvent    ....    139-144,167 

air  in 141 

boiling-point  of    .     .     .     .  100,  136 

buoyancy  of 148-151 

composition  of      135-136, 153, 167 

condensation  of 136 

density  of 137, 150 

diffuaibility 139 

displacement  on  ....  149-150 
effects  of,  upon  life-develop- 
ment    151-152 

effects   of   varying   tempera- 
tures upon 136-138 

energy  in 137-138 

erosive  power  of  ....  278-280 

evaporation  of     ...      101-107, 

136, 166,  278,  385,  528 

expansion  of   ...    136-138, 167 

freezing  of.     .       138,141,167,279 

heat-absorption  of   .    138-139,347 

infection  of      .      205-206, 447-449 

purification     of     polluted 

water 205-206 

life  in     .     .     .       151-152,400-401 
of  land  due  to  ocean-evapo- 
ration       16(> 

physical  properties  of  .     .     .     151 

power  of  running     .     .     .  174-176 

pressure  in       .       146-14S,  1(17   KiS 

transmission  of     .     147-148,168 

qualities  of 144 

soil-  ....      196-198,311-313, 
319, 324-326 


Water  —  Continued 

solutions  in     .       141-142, 167:  278 

sphere  of  activity  of     .      101-1'J7, 

196-206 

evaporation 101-107 

condensation  into  clouds  104 
precipitation  as  rain.  etc.  .  104 
run-off  as  lakes  and  rivers 

200-206 
sinkage   as   artesian   wells, 

springs,  etc.       .     .     .  196-198 

submergence  in     150-151,167-168 

submarine  .     .     .    150-151,167 

suspension  of  matter  in     .11-'    lit 

temperatures  of   .     .  136-138,  142, 

167 

of  salt  solutions    ....     142 
vaporizing  of  ...      98-100, 136 

volume  of 137, 167 

Waterfalls :>-''- 

Waterspouts 231,245 

Waterways     .       17, 19, 152-167, 169, 

171-174,  176^208,  213,  249-251, 

256-258,  514,  531-535,  546-548, 

552 

as  a  means  of  development  .  190 
as  a  means  of  transportation  196 
effects  of,  upon  climate  .  241-243 
effects  of,  upon  shores .  .  243-244 
day  vs.  night;  summer 

vs.  winter     ....  '_'•»:!  -'11 
Watt,  James  (inventor  of  steam 

engine) 470 

Waves.     .     .     .       157-161,169,514 
as  builders  and  drst mycrs  of 

land 159-161 

beaches 161,251 

cliffs,     promontories,    sea- 
caves  160 

crest  of 157.  159 

motion  of  water  in  .     .     .  157-158 

"  oil  on  water  " 168 

trough  of 157,  159 

volcanic  action  vs 614 

Wax  405,490 

Weather    .     .     ,      -'<>'.»  287,944  MS 

(rmprratun-  vs.     LMl'l  :M7,  '.M  I    -'»:. 

,  in  -illation  of  air  .    215  •-'!«..  JJI 

winds.     .     .     •    216-231,244 


26 


EVERYDAY  SCIENCE 


References  are  to  pages 


Weather  —  Continued 

barometric  pressure    .     217 
deflection  of  ...  217-220 
warming     of     atmosphere 

209-213,244 

altitude  vs 212 

clouds  as  heat-containers 

210,  244 
insolation     ....  209-210 

latitude  vs 211 

soil  vs. 212-213 

Weathering  (of  rocks)      .     .  279-281 

Wedge 469 

Weight 66,94 

Weight  arm  (in  lever)       ...     464 
Welding  (by  electricity)  ...     487 

"Westerlies" 224 

Whirlpools 165 

Whooping-cough  (bacterial  dis- 
ease)        442 

Winds  .     .     .110, 125, 162-164,  213, 

215-231,  244-245,  279,  281-285, 

470, 472 

adiabatic   cooling   and   heat- 
ing, a  cause  of      ....     125 
affected    by    ocean-currents, 

162-164 
as  carriers  of  deposition    .     .     285 


Wind—  Continued 

as  causes  of  surface-changes 

281-285 

as  transformers  of  energy  .  470 
as  weathering  agency  .  .  .  279 
barometric  pressure  vs.  .  .  217 
circulation  of  air 

110,215-216,244 

deflection  of 217-220 

direction  of 217 

Ferrel's  law 219 

planetary  wind  belts    220-228,  244 

terrestrial 221,  245 

storms 224-228, 245 

Winds,  trade 221 

Wireless    (telegraph    and    tele- 
phone)     495 

Wood  ashes  (fertilizer)    ...     317 

Worms  (invertebrates)     .     .  401-402 

earthworm 401-402 

Yeasts  ....      303,  399, 422,  437 
buds  of 399 

Yellow    fever    (protozoan    dis- 
ease)        401,452 

Yellowstone  Park  (geysers  of)    .     511 


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